Flowmeter

ABSTRACT

For the purpose of solving the above problems, the present invention includes: transmission/reception means provided in a flow path for performing transmission/reception using a state change of fluid; repetition means for repeating the transmission/reception; time measurement means for measuring a time of propagation repeated by the repetition means; flow rate detection means for detecting a flow rate based on a value of the time measurement means; and number-of-times change means for changing to a predetermined number of repetition times. With such a structure, an influence caused by a variation of a flow can be suppressed by changing the number of repetition times so as to be suitable for a variation. As a result, reliable flow rate measurement with a high accuracy can be achieved.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. patent application Ser.No. 10/019,418, entitled “Ultrasonic Flowmeter Having SequentiallyChanged Driving Method”, filed on Dec. 21, 2001, and had its 35 U.S.C.371 requirements met on Mar. 29, 2002, and which claims priority toPCT/JP00/04165, filed on Jun. 23, 2000, as well as claims priority toJapanese Application Nos. 11-177952, filed Jun. 24, 1999; 11-182995,filed Jun. 29, 1999; and 2000-34677, filed Feb. 14, 2000, all of whichare incorporated herein by reference. All of these applications werealso based on Japanese Application Nos. 11-106246, filed Apr. 14, 1999;11-54082, filed Mar. 2, 1999; 11-106247, filed Apr. 14, 1999; and11-12823, filed Jan. 21, 1999, all of which are incorporated herein byreference.

FIELD OF INVENTION

[0002] The present invention relates to a flowmeter for measuring theflow rate of liquid or air. The present invention relates to means formeasuring a flow rate value in an accurate manner even when there is avariation in pressure or temperature.

BACKGROUND OF INVENTION

[0003] Conventionally, such a type of flowmeter is known, for example,in Japanese Laid-Open Publication No. 9-15006. As shown in FIG. 64, theflowmeter includes: a sampling program 2 for reading a measurementvalue, at an interval having a predetermined first sampling time, froman analog flow sensor 1 that measures the flow rate of gas; a consumedgas amount calculation program 3 for calculating the flow rate ofconsumed gas at a predetermined time; a mean value calculation program 4for calculating the mean value of measurement values, which are readfrom the analog flow sensor at the first sampling time, at an intervalof a second sampling time within a predetermined time period; a pressurevariation frequency estimation program 5 for estimating the frequency ofa pressure variation based on an output of the flow sensor; and a RAM 6which functions as a memory. Herein, reference numeral 7 a denotes a CPUfor executing the programs, and reference numeral 7 b denotes a ROM forstoring the programs. In such a structure, a measurement process isperformed such that the predetermined measurement time is equal to orlonger than a single cycle of the vibration frequency of a pump or is amultiple of the cycle. Averaging is performed to suppress variation inthe flow rate.

[0004] As another conventional example, the invention disclosed inJapanese Laid-Open Publication No. 10-197303 is known. As shown in FIG.65, the flowmeter includes: flow rate detection means 8 for detectingthe flow rate; frequency detection means 9 for detecting the frequencyof a variation of a flow; and measurement time set means 10 for settingthe measurement time for flow rate detection to about a multiple of onecycle of the variation frequency. Herein, reference numeral 11 denotesflow rate calculation means; 12 denotes measurement start means; 13denotes signal processing means; and 14 denotes a flow rate. With thisstructure, the flow rate is measured in accordance with the frequency ofa variation waveform, whereby a correct flow rate measurement isachieved within a short time period.

[0005] As still another conventional example, the invention disclosed inJapanese Laid-Open Publication No. 11-44563 is known. As shown in FIG.66, the flowmeter includes: flow rate detection means 15 for detectingthe flow rate; variation detection means 16 for detecting a variationwaveform of the flow rate of fluid; pulse measurement means 17 forstarting the measurement of the flow rate detection means when analternating component of the variation waveform is in the vicinity ofzero; and flow rate calculation means 18 for processing a signal fromthe flow rate detection means. Herein, reference numeral 19 denotes asignal processing circuit; 20 denotes a time measurement circuit; 21denotes a trigger circuit; 22 denotes a transmission circuit; 23 denotesa comparison circuit; 24 denotes an amplification circuit; 25 denotes aswitch; 26 denotes a measurement start signal circuit; and 27 denotesstart-up means; 28 denotes a flow path. In this structure, the flow ratenear the average of the variation waveforms is measured, whereby acorrect flow rate measurement is achieved within a short time period.

[0006] As yet another conventional example, the invention disclosed inJapanese Laid-Open Publication No. 8-271313 is known. As shown in FIG.67, whether or not a flow rate value has been detected in flow sensormeasurement (29) is confirmed (30). Until a flow rate is confirmed tohave been detected, the process does not proceed, and the measurementwith the flow sensor is continued. Once a flow rate is found, it isdetermined whether or not the flow rate Q is equal to or higher than apredetermined value (31). When the flow rate Q is equal to or higherthan the predetermined value, it is further determined whether or notthe pressure variation surpasses a predetermined-value Cf (32). When thepressure variation does not surpass a predetermined value Cf,measurement 34 is performed with a piezoelectric film sensor of afluidic flowmeter. When the pressure variation surpasses a predeterminedvalue Cf, it is confirmed if the pressure variation surpasses a secondpredetermined value (33). When the pressure variation surpasses thesecond predetermined value, the measurement (34) is performed with thepiezoelectric film sensor of the fluidic flowmeter. When the pressurevariation does not surpass the second predetermined value, themeasurement (29) is performed with the flow sensor.

[0007] As shown in FIG. 68, ultrasonic wave transducers 51 and 52 areprovided in a flow rate measurement section 50 so as to oppose thedirection of a flow. A control section 53 starts a timer 54, andsimultaneously, outputs a transmission signal to a driver circuit 55. Anultrasonic wave is transmitted from the ultrasonic wave transducer 51which received an output of the driver circuit 55. The ultrasonic waveis received by the ultrasonic wave transducer 52. A reception detectioncircuit 56 which received an output of the ultrasonic wave transducer 52detects the ultrasonic wave and stops the timer 54. By such anoperation, a time (t1) spent from a time when an ultrasonic wave istransmitted from the ultrasonic wave transducer 51 to a time when thewave is detected by the ultrasonic wave transducer 52 is measured. Next,a switching circuit 58 is operated based on a signal from the controlsection 53, such that the driver circuit 55 and the ultrasonic wavetransducer 52 are connected, and the reception detection circuit 56 andthe ultrasonic wave transducer 51 are connected. Under this state,transmission and reception of an ultrasonic wave is performed again tomeasure a time (t2) spent from a time when an ultrasonic wave istransmitted from the ultrasonic wave transducer 52 to a time when thewave is detected by the ultrasonic wave transducer 51. Based on the twopropagation times (t1) and (t2), a calculation section 57 calculates theflow rate from a difference between inverse numbers of the propagationtimes.

[0008] As a conventional example of this type of flowmeter, theinvention disclosed in Japanese Laid-Open Publication No. 6-269528 isknown.

[0009] However, in the first of the above conventional inventions, thegas flow rate is measured by using a mean value. Therefore, measurementover a long time period is necessary in order to obtain a reliable meanvalue, and hence such flow rate measurement cannot be performed within avery short space of time. In the second of the above conventionalinventions, measurement cannot deal with a variation in frequency. Inthe third and fourth conventional inventions, the method for measuringthe flow rate must be changed according to the presence/absence of apressure variation, and it is necessary to provide two means, pressuremeasurement means and flow rate measurement means. In the first to forthinventions, when any abnormality occurs, measurement either cannot beperformed, or can be performed but with decreased accuracy.

[0010] Still further, in the above conventional structures, whenreceiving a signal, if noise which is in synchronization with themeasurement frequency or transmission frequency of an ultrasonic wave ispresent, the noise is superposed on the signal always at the same phasewhen the propagation time is the same. The noise is counted as ameasurement error, and accordingly, correct measurement cannot beperformed. Moreover, when the propagation time is varied due to avariation in temperature or the like, the phase at which noise issuperposed is varied, and accordingly, a measurement error is varied. Asa result, a correction value cannot be stabilized. Furthermore, sincethe measurement resolution is determined based on the resolution of thetimer 54, simply averaging the measurement values cannot increase theaccuracy of measurement. Thus, it is necessary to increase theresolution of the timer 54 in order to perform measurement whichrequires the resolution. When the operation clock of the timer 54 isincreased so as to have a high frequency, various problems occur, i.e.,an increase in current consumption, an increase in high-frequency noise,and an increase in size of circuitry. Thus, there exists an objective toincrease the resolution of measurement with a timer which operates at alow frequency in order to increase the measurement accuracy.

[0011] In the fifth conventional invention, a delay means is insertedbetween a control section and a drive circuit, and the amount of delayis changed such that a reflected wave is avoided. In this way, an effectby the reflected wave is reduced. For example, the ultrasonic wavetransducer at a receiving side is vibrated due to noise generated whenthe ultrasonic wave is transmitted. Thus, a variation in thesignal-reception detecting time, which is caused by superposition ofreverberation of this vibration on the ultrasonic wave signal, cannot bedecreased.

[0012] The present invention seeks to solve the above problems. A firstobjective of the present invention is to set an optimum number of timesthat the measurement is repeated according to a variation of a flow bydetecting a variation frequency using software but without usingadditional variation detecting device, and successively changing thenumber of repetition times. Further, it is sought to achieve ameasurement flow rate in a reliable and accurate manner within a veryshort space of time even when there is a change in pressure variationand variation frequency. A second objective of the present invention isto instantaneously perform highly accurate flow-rate measurements byswitching so as to detect a variation with transmission/reception meanswithout using an additional variation detecting device and performingmeasurement processing in synchronization with a variation. A thirdobjective of the present invention is to perform highly accurateflow-rate measurement, even when any abnormality occurs in themeasurement process, by quickly detecting the abnormality withmeasurement monitoring means and appropriately processing themeasurement. A fourth objective of the present invention is to performflow-rate measurement in a reliable and accurate manner within a veryshort space of time by using instantaneous flow rate measurement meansand digital filter means. A fifth objective of the present invention isto measure a flow rate value with a high accuracy even when there is avariation in temperature.

SUMMARY OF INVENTION

[0013] In order to solve the above problems, a flowmeter of the presentinvention includes: transmission/reception means provided in a flow pathfor performing transmission/reception using a state change of fluid;repetition means for repeating the transmission/reception; timemeasurement means for measuring a time or propagation repeated by therepetition means; flow rate detection means for detecting a flow ratebased on a value of the time measurement means; and number-of-timeschange means for changing to a predetermined number of repetition times.The number of repetition times is changed to a number suitable for avariation such that an influence of a variation of a flow can besuppressed. As a result, reliable flow rate measurement with a highaccuracy can be achieved.

[0014] The flowmeter includes a pair of transmission/reception meanswhich utilize propagation of an ultrasonic wave as the state change offluid. Thus, by using the sonic wave transmission/reception means,propagation of a sonic wave can be performed even when a state changeoccurs in the fluid. Moreover, by changing the number of repetitiontimes to a number suitable for the variation, reliable flow ratemeasurement with a high accuracy can be achieved.

[0015] The flowmeter includes transmission/reception means whichutilizes propagation of heat as the state change of fluid. Thus, byusing the heat transmission/reception means, propagation of heat can beperformed even when a state change occurs in the fluid. Moreover, bychanging the number of repetition times to a number suitable for thevariation, reliable flow rate measurement with a high accuracy can beachieved.

[0016] The flowmeter includes: elapsed time detection means fordetecting halfway information for a propagation time which is repeatedlymeasured by the repetition means; frequency detection means fordetecting a frequency of a flow rate variation from information of theelapsed time detection means; and number-of-times change means forsetting a measurement time so as to be substantially a multiple of thefrequency detected by the frequency detection means. Thus, it is notnecessary to provide specific detection means. Before flow ratedetection is performed, the frequency of a variation is detected fromhalfway information of the time measurement means, and the measurementtime can be set so as to be a multiple of a cycle of the frequency. As aresult, reliable flow rate measurement with a high accuracy can beachieved.

[0017] The flowmeter includes: data holding means for holding at leastone or more propagation time of repeatedly-performedtransmission/reception which is obtained by the elapsed time detectionmeans; and frequency detection means for detecting a frequency bycomparing the data held by the data holding means and measuredpropagation time data. Time measurement information at each moment isheld and compared by the data holding means, whereby the frequency canbe detected.

[0018] The number-of-times change means is operated in predeterminedprocessing. Since the number-of-times change means is operated only whenpredetermined processing is performed, the processing in thenumber-of-times change means can be limited to the required minimum.Thus, the amount of consumed power can be considerably reduced.

[0019] The number-of-times change means is operated at eachpredetermined flow rate measurement. Thus, the number of repetitiontimes is changed at every predetermined flow rate measurement, wherebythe flow rate can be measured with a high accuracy in a stable mannereven in a flow that varies greatly.

[0020] The number-of-times change means is performed before flow ratemeasurement processing. Since the number of repetition times is set to apredetermined number of times before flow rate measurement is performed,the flow rate measurement can be performed with a high accuracy in areliable manner.

[0021] Predetermined processing includes operations of abnormalitydetermination means for determining abnormality in flow rate from themeasured flow rate; and flow rate management means for managing a usestate for a flow rate from a measured flow rate. Since the number ofrepetition times is changed only when the abnormality determinationprocessing and the flow rate management processing are performed, theprocessing of changing the number of repetition times is limited to therequired minimum. Thus, the amount of consumed power can be decreased.

[0022] The number of repetition times which is adjusted the frequencyobtained by the frequency detection means is used in next flow ratemeasurement. Since the number of repetition times is used in the nextmeasurement, it is not necessary to perform repetitious measurement forfrequency detection. Thus, the amount of consumed power can bedecreased.

[0023] The number-of-times change means is operated when the measuredflow rate is lower than a predetermined flow rate. Since the number ofrepetition times is changed only when the flow rate is equal to or lowerthan a predetermined flow rate, but this processing is not performedwhen the flow rate is high, the amount of consumed power can bedecreased.

[0024] A flowmeter of the present invention includes:transmission/reception means provided in a flow path for performingtransmission/reception using a state change of fluid; time measurementmeans for measuring a propagation time transmitted/received by thetransmission/reception means; flow rate detection means for detecting aflow rate based on a value of the time measurement means; variationdetection means for measuring a variation in the flow path by thetransmission/reception means; and measurement control means for startingmeasurement in synchronization with a timing of a variation of thevariation detection means. Since a variation in the flow path ismeasured by transmission/reception means, it is not necessary to provideanother sensor for detecting a variation. Thus, the size of theflowmeter can be decreased, and the structure of the flow path can besimplified. In addition, the flow rate can be measured with a highaccuracy in a reliable manner within a short space of time even when avariation occurs.

[0025] The flowmeter includes a pair of transmission/reception meanswhich utilize propagation of an ultrasonic wave as the state change offluid. Thus, a state change of fluid can be detected by the sonic wavetransmission/reception means. Accordingly, the measurement can bestarted in synchronization with a timing of variation. As a result, theflow rate can be measured with a high accuracy in a reliable manner.

[0026] The flowmeter includes transmission/reception means whichutilizes propagation of heat as the state change of fluid. Thus, a statechange of fluid can be detected by the heat transmission/receptionmeans. Accordingly, the measurement can be started in synchronizationwith a timing of variation. As a result, the flow rate can be measuredwith a high accuracy in a reliable manner.

[0027] The flowmeter includes: first vibration means and secondvibration means provided in a flow path for transmitting/receiving ansonic wave; switching means for switching an transmission/receptionoperation of the first vibration means and the second vibration means;variation detection means for detecting a pressure variation in a flowpath of at least one of the first vibration means and the secondvibration means; time measurement means for measuring a propagation timeof a sonic wave transmitted/received by the first vibration means andthe second vibration means; measurement control means for performingcontrol where, when an output of the variation detection means shows apredetermined change, the measurement means measures a first measurementtime T1 of propagation from the first vibration means at an upstreamside in the flow path to the second vibration means at a downstream sidein the flow path, and when the output of the variation detection meansshows a change opposite to the predetermined change, the measurementmeans measures a second measurement time T2 of propagation from thesecond vibration means at a downstream side in the flow path to thefirst vibration means at an upstream side in the flow path; flow ratedetection means for calculating a flow rate using the first measurementtime T1 and the second measurement time T2. Since the measurement isperformed at a time when a change in a pressure variation is inverted,the phases of the pressure variation and the timing of the measurementcan be shifted. As a result, a measurement error caused by a pressurevariation can be offset.

[0028] The flowmeter includes: measurement control means for performingmeasurement control where measurement of the first measurement time T1is started when an output of the variation detection means shows apredetermined change and measurement of the second measurement time T2is started when the output of the variation detection means shows achange opposite to the predetermined change, and measurement controlwhere, in a next measurement, measurement of the first measurement timeT1 is started when the output of the variation detection means shows achange opposite to the predetermined change and measurement of thesecond measurement time T2 is started when the output of the variationdetection means shows the predetermined change; and flow ratecalculation means for calculating the flow rate by successivelyaveraging a first flow rate obtained by using the previous firstmeasurement time T1 and previous second measurement time T2 whilealternately changing start of measurement and a second flow rateobtained by using next first measurement time T1 and next secondmeasurement time T2. Thus, the timing for measurement is changed asdescribed above in order to perform measurement for the firstmeasurement time T1 and the second measurement time T2. As a result,even when a pressure variation is asymmetrical between a high pressureside and a low pressure side, an influence of such a pressure variationcan be offset.

[0029] The flowmeter includes repetition means for performingtransmission/reception a plurality of times. Thus, averaging can beperformed by increasing the number of times of measurement, and as aresult, reliable flow rate measurement can be performed.

[0030] The flowmeter includes repetition means for performingtransmission/reception a plurality of times over a time period which isa multiple of a variation cycle. Thus, a pressure variation can beaveraged by measuring according to the variation frequency. As a result,a stable flow rate can be measured.

[0031] The flowmeter includes repetition means for startingtransmission/reception measurement when an output of the variationdetection means shows a predetermined change and repeating thetransmission/reception measurement with a sonic wave until the output ofthe variation detection means shows the same change as the predeterminedchange. Thus, the start and stop of the measurement can be madeconformable to the frequency of a pressure variation, Therefore, avariation frequency can be measured, and a pressure variation isaveraged. As a result, a stable flow rate can be measured.

[0032] The flowmeter includes selection means for switching a case wherethe first vibration means and second vibration means are used fortransmission/reception of a sonic wave and a case where the firstvibration means and second vibration means are used for detection of apressure variation. Thus, at least one of the first vibration means andthe second vibration means is used for pressure detection. As a result,both the flow rate measurement and the pressure measurement can besimultaneously achieved.

[0033] The flowmeter includes variation detection means for detecting acomponent of an alternating component of a variation waveform which isin the vicinity of zero. Thus, a variation is detected in the vicinityof a zero component of the variation, and hence the measurement can bestarted in the vicinity of zero variation within a time to perform flowrate measurement. Therefore, by performing the flow rate measurementwithin a time when a variation is small, the measurement can bestabilized even when a variation occurs in a fluid.

[0034] The flowmeter includes: frequency detection means for detectingthe frequency of a signal of the variation detection means; andmeasurement control means for starting measurement only when thefrequency detected by the frequency detection means is a predeterminedfrequency. Thus, by starting the measurement only when the frequency isa predetermined frequency, measurement can be performed when apredetermined variation occurs. As a result, a stable flow rate can bemeasured.

[0035] The flowmeter includes detection cancellation means forautomatically starting measurement after a predetermined time periodwhen a signal of the variation detection means is not detected. Thus,even after a variation disappears, the flow rate can be automaticallymeasured when a predetermined time arrives.

[0036] The transmission/reception means and the first and secondvibration means include piezoelectric transducers. Thus, when thepiezoelectric transducer is used, an ultrasonic wave is used fortransmission/reception while a pressure variation can be detected.

[0037] A flowmeter of the present invention includes:transmission/reception means provided in a flow path for performingtransmission/reception using a state change of fluid; repetition meansfor repeating signal propagation by the transmission/reception means;time measurement means for measuring a propagation time duringrepetition by the repetition means; flow rate detection means fordetecting a flow rate based on a value of the time measurement means;variation detection means for detecting a fluid variation in a flowpath; measurement control means for controlling each of the above means;and measurement monitoring means for monitoring abnormality in each ofthe above means. Thus, when there is a variation in a flow in the flowpath, the flow rate is measured according to the variation, whileabnormality can be quickly detected by the measurement monitoring means.Accordingly, handling of abnormality can be correctly performed, and ameasured value becomes stable. As a result, the flow rate can bemeasured with a high accuracy, and the reliability of the measurementcan be improved.

[0038] The flowmeter includes a pair of transmission/reception meanswhich utilize propagation of an ultrasonic wave as the state change offluid. Since a sonic wave is used, the flow rate measurement can beperformed even when there is a variation in fluid. Further, handling ofabnormality can be correctly performed by the measurement monitoringmeans. As a result, the reliability of the measurement can be improved.

[0039] The flowmeter includes transmission/reception means whichutilizes propagation of heat as the state change of fluid. Since heatpropagation is used, the flow rate measurement can be performed evenwhen there is a variation in fluid. Further, handling of abnormality canbe correctly performed by the measurement monitoring means. As a result,the reliability of the measurement can be improved.

[0040] The flowmeter includes: a pair of transmission/reception meansprovided in a flow path for transmitting/receiving a sonic wave;repetition means for repeating signal propagation of thetransmission/reception means; time measurement means for measuring apropagation time of a sonic wave during the repetition by the repetitionmeans; flow rate detection means for detecting the flow rate based on avalue of the time measurement means; variation detection means fordetecting a fluid variation in a flow path; measurement control meansfor controlling each of the above means; and measurement monitoringmeans for monitoring abnormality in a start signal which directs startof transmission of a sonic wave at a first output signal of thevariation detection means after a direction signal of the measurementcontrol means, and abnormality in an end signal which directs end ofrepetition of the transmission/reception of the sonic wave at secondoutput signal of the variation detection means. Thus, when there is avariation in fluid in the flow path, the measurement can be performed insynchronization with the frequency of the variation, and abnormality canbe detected by the measurement monitoring means. Therefore, a flow ratecan be measured with a high accuracy, and a reliable measured value canbe obtained. In addition, handling of abnormality can be correctlyperformed, and the reliability of the measured flow rate value can beimproved.

[0041] The flowmeter includes measurement monitoring means for directinga start of transmission of a sonic wave after a predetermined time whena start signal is not generated within a predetermined time period aftera direction of the measurement control means. Thus, even when there isno variation, and there is no start signal within a predetermined timeperiod, the flow rate can be measured at every predetermined time, andloss of data can be prevented.

[0042] The flowmeter includes measurement monitoring means for directingstart of transmission of a sonic wave after a predetermined time when astart signal is not generated within a predetermined time period after adirection of the measurement control means, and for performingmeasurement a predetermined number of repetition times. Thus, even whenthere is no variation, and there is no start signal within apredetermined time period, the flow rate can be measured for apredetermined number of repetition times at every predetermined time,and loss of data can be prevented.

[0043] The flowmeter includes measurement monitoring means which doesnot perform measurement until a next direction of the measurementcontrol means when a start signal is not generated within apredetermined time period after a direction of the measurement controlmeans. By suspending the operation until a next measurement direction,unnecessary measurement is not performed, whereby the amount of consumedpower can be decreased.

[0044] The flowmeter includes measurement monitoring means whichterminates reception of a sonic wave when an end signal is not generatedwithin a predetermined time after a start signal. Since the reception ofthe sonic wave is forcibly terminated, the measurement is not suspendedwhile waiting for the end signal. Thus, the measurement can proceed to anext process, and a stable measurement operation can be performed.

[0045] The flowmeter includes measurement monitoring means whichterminates reception of a sonic wave and outputs a start signal again,when an end signal is not generated within a predetermined time after astart signal. Since the reception of the sonic wave is forciblyterminated, the measurement is not suspended while waiting for the endsignal. Further, a start signal is output again so as to performre-measurement. Thus, a stable measurement operation can be performed.

[0046] The flowmeter includes measurement monitoring means for stoppingtransmission/reception processing when abnormality occurs in the numberof repetition times. Since the measurement is stopped when the number ofrepetition times is abnormal, only data with a high accuracy can be usedto perform flow rate measurement.

[0047] The flowmeter includes measurement monitoring means whichcompares a first number of repetition times for measurement where asonic wave is transmitted from a first one of the pair oftransmission/reception means and received by the secondtransmission/reception means and a second number of repetition times formeasurement where a sonic wave is transmitted from the secondtransmission/reception means and received by the firsttransmission/reception means, and again outputs a start signal when thedifference between the first and second numbers of repetition times isequal to or greater than a predetermined number of times. Thus,re-measurement is performed when the number of repetition times isgreatly different, whereby measurement with a high accuracy can beperformed with a stable variation frequency.

[0048] The flowmeter includes repetition means for setting the number ofrepetition times such that a first number of repetition times formeasurement where a sonic wave is transmitted from first one of the pairof transmission/reception means and received by the secondtransmission/reception means is equal to a second number of repetitiontimes for measurement where a sonic wave is transmitted from the secondtransmission/reception means and received by the firsttransmission/reception means. Thus, by employing the same number ofrepetition times, a predetermined flow rate measurement can be performedeven when a variation frequency is unstable.

[0049] The flowmeter includes measurement monitoring means formonitoring the number of times that a start signal is output again so asto be limited to a predetermined number of times or less, such that theoutputting of the start signal is not permanently repeated. Thus, bylimiting the number of times of re-measurement, the processing isprevented from continuing permanently. As a result, stable flow ratemeasurement can be performed.

[0050] The flowmeter measures a flow rate from a difference betweeninverse numbers of propagation times measured while repeatingtransmission/reception of an ultrasonic wave a plurality of number oftimes. Thus, when an ultrasonic wave is used, transmission/reception canbe performed without being affected by a variation frequency in the flowpath. Further, the flow rate is measured from the difference of inversenumbers of propagation times which are measured while repeating thetransmission/reception, whereby even a variation of a long cycle can bemeasured by units of one cycle. In addition, the difference of thepropagation times which is caused by a variation can be offset by usingthe difference of inverse numbers.

[0051] A flowmeter of the present invention includes: instantaneous flowrate detection means for detecting an instantaneous flow rate;fluctuation determination means for determining whether or not there isa pulse in a flow rate value; and at least one or more stable flow ratecalculation means for calculating a flow rate value using differentmeans according to a determination result of the fluctuationdetermination means. Thus, by determining a variation in a measured flowrate and switching the flow rate calculation means, the flow rate can becalculated by one flow rate measurement means according to the amount ofthe variation in a reliable manner.

[0052] A flowmeter of the present invention includes: instantaneous flowrate detection means for detecting an instantaneous flow rate; filterprocessing means for performing digital-filter processing of a flow ratevalue; and stable flow rate calculation means for calculating a flowrate value using the filter processing means. Thus, when the digitalfilter processing is performed, a calculation equivalent to an averagingprocess can be performed without using a large number of memories forstoring data. Moreover, the filter characteristic can be modified bychanging one variable, i.e., a filter coefficient.

[0053] The flowmeter includes stable flow rate calculation means forcalculating a stable flow rate value using the digital filter processingmeans when the fluctuation determination means determines that there isa pulse. Thus, when a pulse occurs, a sharp filter characteristic isselected so as to render a large pulse stable, and the filter processingcan be performed only when a pulse occurs.

[0054] The fluctuation determination means determines whether or not avariation amplitude of a flow rate value is equal to or greater than apredetermined value. Thus, a pulse can be determined based on thevariation amplitude of the pulse, whereby the filter processing can bemodified according to the variation amplitude of the pulse.

[0055] The filter processing means modifies a filter characteristicaccording to a variation amplitude of a flow rate value. Since thefilter characteristic is changed according to the variation amplitude ofa flow rate value, the filter characteristic can be quickly modified soas to be a sufficiently relaxed filter characteristic that allows avariation according to a variation in a flow rate when the variation issmall, and when the variation is large, a sharp filter characteristic isselected such that a variation of the flow rate due to a pulse can besignificantly suppressed.

[0056] The filter processing is performed only when a flow rate valuedetected by the instantaneous flow rate detection means is low. Sincethe filter processing is performed only when the flow rate is low, avariation of the flow rate can be quickly handled when the flow rate ishigh, and an influence of fluctuation which is caused when the flow rateis low can be significantly suppressed.

[0057] Filter processing means modifies a filter characteristicaccording to a flow rate value. Since the filter characteristic ischanged according to the flow rate value, filter processing is performedonly when the flow rate is low, a variation of the flow rate can bequickly handled when the flow rate is high, and an influence offluctuation which is caused when the flow rate is low can besignificantly suppressed.

[0058] Filter processing means modifies a filter characteristicaccording to an interval of a flow rate time of the instantaneous flowrate detection means. Thus, by changing the filter characteristicaccording to an interval of the flow rate detection time, the variationcan be suppressed with a relaxed filter characteristic when themeasurement interval is short or with a sharp filter characteristic whenthe measurement interval is long.

[0059] The flowmeter includes filter processing means which modifies afilter characteristic such that a cut-off frequency of the filtercharacteristic becomes high when the flow rate is high, and whichmodifies a filter characteristic such that the filter characteristic hasa low cut-off frequency when the flow rate is low. Thus, the responsecharacteristic is increased when the flow rate is high, and thefluctuation is suppressed when the flow rate is low.

[0060] A filter characteristic is modified such that a variationamplitude of a flow rate value calculated by the stable flow ratecalculation means is within a predetermined value range. Since thefilter characteristic is modified such that the variation amplitude iswithin a predetermined value range, the flow rate variation can besuppressed so as to be always equal to or smaller than a predeterminedvalue.

[0061] An ultrasonic wave flowmeter which detects a flow rate by usingan ultrasonic wave is used as the instantaneous flow rate detectionmeans. Thus, by using an ultrasonic wave flowmeter, an instantaneousflow rate can be measured even when a large flow rate variation occurs.Thus, from the flow rate value, a stable flow rate can be calculated.

[0062] A heat-based flowmeter is used as the instantaneous flow ratedetection means. When the heat-based flowmeter is used, an instantaneousflow rate can be measured even when a large flow rate variation occurs.Thus, a stable flow rate can be calculated from the flow rate value.

[0063] A flowmeter of the present invention includes: a flow ratemeasurement section through which fluid to be measured flows; a pair ofultrasonic wave transducers provided in the flow rate measurementsection for transmitting/receiving an ultrasonic wave; a driver circuitfor driving one of the ultrasonic wave transducers; a receptiondetecting circuit connected to the other ultrasonic wave transducer fordetecting an ultrasonic wave signal; a timer for measuring a propagationtime of the ultrasonic wave signal; a control section for controllingthe driver circuit; a calculation section for calculating a flow ratefrom an output of the timer; and periodicity change means forsequentially changing a driving method of the driver circuit, whereinthe control section controls the periodicity change means such that thefrequency of flow rate measurement is sequentially a changed in order toprevent the frequency of the measurement from being constant. Thus,noise which is in synchronization with a measurement frequency or atransmission frequency of an ultrasonic wave is never in the same phasebut dispersed when the ultrasonic wave is received. Therefore, ameasurement error can be decreased.

[0064] A flowmeter of the present invention includes: a flow ratemeasurement section through which fluid to be measured flows: a pair ofultrasonic wave transducers provided in the flow rate measurementsection for transmitting/receiving an ultrasonic wave; a driver circuitfor driving one of the ultrasonic wave transducers; a receptiondetecting circuit connected to the other ultrasonic wave transducer fordetecting an ultrasonic wave signal; a control section for controllingthe driver circuit for a predetermined number of times so as to drivethe ultrasonic wave transducers again in response to an output of thereception detecting circuit; a timer for measuring an elapsed time forthe predetermined number of times; a calculation section for calculatinga flow rate from an output of the timer; and periodicity change meansfor sequentially changing a driving method of the driver circuit,wherein, in response to receipt of an output of the reception detectingcircuit, the control section changes the periodicity change means atevery receipt detection of the reception detecting circuit such that thefrequency is not kept constant. Thus, the periodicity change means canbe operated with a plurality of settings for measurement within one flowrate measurement cycle. As a result, noise is dispersively averaged in ameasurement result, and a reliable measurement result can be obtained.

[0065] The periodicity change means switchingly outputs a plurality ofoutput signals having different frequencies; and the control sectionchanges a frequency setting of the periodicity change means at everymeasurement so as to change a driving frequency of the driver circuit.Thus, by changing the driving frequency, the reception detecting timingcan be changed by a time corresponding to a frequency variation of adriving signal. Thus, noise which is in synchronization with ameasurement frequency or a transmission frequency of an ultrasonic waveis never in the same phase but dispersed when the ultrasonic wave isreceived. Therefore, a measurement error can be decreased.

[0066] The periodicity change means outputs output signals having thesame frequency and a plurality of different phases; and the controlsection operates such that a phase setting for the output signal of theperiodicity change means is changed at every measurement and a drivingphase of the driver circuit is changed. Thus, by changing the drivingphase, the reception detecting timing can be changed by a timecorresponding to a phase variation of a driving signal. Thus, noisewhich is in synchronization with a measurement frequency or atransmission frequency of an ultrasonic wave is never in the same phasebut dispersed when the ultrasonic wave is received. Therefore, ameasurement error can be decreased.

[0067] The frequency change means outputs a synthesized signal obtainedby superposing a signal of a first frequency which is an operationfrequency of the ultrasonic wave transducers and a signal of a secondfrequency which is different from the first frequency; and the controlsection outputs, through the driver circuit, at every measurement, anoutput signal where the second frequency of the periodicity change meansis changed. Thus, the periodicity of the flow rate measurement can bedisturbed. As a result, noise which is in synchronization with ameasurement frequency or a transmission frequency of an ultrasonic waveis never in the same phase but dispersed when the ultrasonic wave isreceived. Therefore, a measurement error can be decreased.

[0068] The periodicity change means switches the setting between a casewhere there is a second frequency and a case where there is not a secondfrequency. Thus, since the reception detecting timing is changed bychanging the vibration of the ultrasonic wave transducer that transmitsan ultrasonic wave, the periodicity of the flow rate measurement can bedisturbed. As a result, noise which is in synchronization with ameasurement frequency or a transmission frequency of an ultrasonic waveis never in the same phase but dispersed when the ultrasonic wave isreceived. Therefore, a measurement error can be decreased.

[0069] The periodicity change means changes the phase setting of thesecond frequency. Thus, since the reception detecting timing is changedby changing the vibration of the ultrasonic wave transducer thattransmits an ultrasonic wave, the periodicity of the flow ratemeasurement can be disturbed. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed/averagedwhen the ultrasonic wave is received. Therefore, a measurement error canbe decreased.

[0070] The periodicity change means changes the frequency setting of thesecond frequency. Thus, since the reception detecting timing is changedby changing the vibration of the ultrasonic wave transducer thattransmits an ultrasonic wave, the periodicity of the flow ratemeasurement can be disturbed. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed when theultrasonic wave is received. Therefore, a measurement error can bedecreased.

[0071] The periodicity change means includes a delay section capable ofsetting different delay times; and the control section changes thesetting of the delay at each transmission of an ultrasonic wave or ateach receipt detection of an ultrasonic wave. Thus, in one measurementoperation, reverberation of an ultrasonic wave transmitted in animmediately-previous measurement and an influence of tailing of theultrasonic wave transducers can be dispersed, whereby a measurementerror can be decreased.

[0072] The cycle width changed by the periodicity change means is amultiple of a value corresponding to a variation of a propagation timewhich is caused by a measurement error. Thus, when the measured valuesfor all the settings are summed up and averaged, an error can besuppressed to a minimum.

[0073] The cycle width changed by the periodicity change means is equalto a cycle of a resonance frequency of the ultrasonic wave transducers.Thus, in a value obtained by summing up and averaging the measuredvalues for all the settings, a measurement error which may be caused byreverberation of an ultrasonic wave or tailing of the ultrasonic wavetransducers is minimum. Thus, the measurement error can be decreased.

[0074] The order of patterns for changing the periodicity is the samefor both measurement in a upstream direction and measurement in adownstream direction. Thus, the measurement with an ultrasonic wavetransmitted toward the upstream side and the measurement with anultrasonic wave transmitted toward the downstream side are alwaysperformed under the same conditions. Hence, even when there is avariation in the flow rate, a reliable measurement result can beobtained.

[0075] The predetermined number of times is a multiple of a changenumber of the periodicity change means. Thus, all the setting values ofthe periodicity change means are uniformly set within a single flow ratemeasurement operation. As a result, a reliable measurement result can beobtained.

[0076] A flowmeter of the present invention includes: a flow ratemeasurement section through which fluid to be measured flows; a pair ofultrasonic wave transducers provided in the flow rate measurementsection for transmitting/receiving an ultrasonic wave; a driver circuitfor driving one of the ultrasonic wave transducers; a receptiondetecting circuit connected to the other ultrasonic wave transducer fordetecting an ultrasonic wave signal; a first timer for measuring apropagation time of the ultrasonic wave signal; a second timer formeasuring a time period from when the reception detecting circuitdetects a receipt to when a value of the first timer changes; a controlsection for controlling the driver circuit; and a calculation sectionfor calculating a flow rate from outputs of the first timer and secondtimer, wherein the second timer is corrected by the first timer. Sincethe flow rate calculation is performed using a value obtained bysubtracting a value of the second timer from a value of the first timer,the time measurement resolution is equal to that of the second timer.Further, since the operation time of the second timer is very short, theamount of consumed power can be decreased. A thus, a flowmeter with highresolution which consumes a small amount of power can be realized.Furthermore, a correct flow rate measurement can be achieved so long asthe second timer operates in a stable manner after the correction ismade until flow rate measurement is performed. Therefore, a correctmeasurement can be performed even when the second timer lacks long termstability. Thus, a flowmeter with a high accuracy can be realized withordinarily-employed parts.

[0077] The flowmeter includes a temperature sensor, wherein the secondtimer is corrected by the first timer when an output of the temperaturesensor varies so as to be equal to or greater than a set value. Thus,even when the second timer has a characteristic which varies accordingto a variation in the temperature, the second timer is corrected everytime a temperature variation occurs, whereby correct measurement can beperformed. Furthermore, such a correction is made only when it isnecessary, the amount of consumed power can be decreased.

[0078] The flowmeter includes a voltage sensor for detecting the powersupply voltage of the circuit, wherein the second timer is corrected bythe first timer when an output of the voltage sensor varies so as to beequal to or greater than a set value. Thus, even when the second timerhas a characteristic which varies according to a variation in the powersupply voltage, the second timer is corrected every time a variationoccurs in the power supply voltage, whereby correct measurement can beperformed. Furthermore, it is not necessary to periodically make acorrection, the amount of consumed power can be decreased.

[0079] A flowmeter of the present invention includes: a flow ratemeasurement section through which fluid to be measured flows; a pair ofultrasonic wave transducers provided in the flow rate measurementsection for transmitting/receiving an ultrasonic wave; a driver circuitfor driving one of the ultrasonic wave transducers; a receptiondetecting circuit connected to the other ultrasonic wave transducer fordetecting an ultrasonic wave signal; a control section for controllingthe driver circuit for a predetermined number of times so as to drivethe ultrasonic wave transducers again in response to an output of thereception detecting circuit; a timer for measuring an elapsed time forthe predetermined number of times: a calculation section for calculatinga flow rate from an output of the timer; and periodicity stabilizingmeans for sequentially changing a driving method of the driver circuit,wherein the control section controls the periodicity stabilizing meanssuch that a measurement frequency is always maintained to be constant.With this structure, the measurement frequency is always constant evenwhen a propagation time varies. Thus, noise which is in synchronizationwith a measurement frequency or a transmission frequency of anultrasonic wave is always in the same phase when the ultrasonic wave isreceived regardless of a variation in the propagation time. Therefore, ameasurement error can be maintained as a constant value. Accordingly,the flow rate measurement can be stabilized even when the noise has avery long periodic noise.

[0080] The control section includes periodicity stabilizing means formedby a delay section capable of setting different delay times; and thecontrol section changes an output timing of the driver circuit byswitching the delay times. Since the measurement frequency is maintainedto be constant by changing the delay time, the measurement frequency canbe stabilized without giving an influence to driving of the ultrasonicwave transducers.

[0081] The control section controls the driver circuit such that ameasurement time is maintained to be constant. Thus, the measurementfrequency can be maintained to be constant with a simple calculationwithout calculating a propagation time for each ultrasonic wavetransmission.

BRIEF DESCRIPTION OF DRAWINGS

[0082]FIG. 1 is a block diagram showing a flowmeter according toembodiment 1 of the present invention.

[0083]FIG. 2 is a timing chart illustrating an operation of theflowmeter of embodiment 1.

[0084]FIG. 3 is a variation waveform graph for illustrating theoperation of the flowmeter of embodiment 1.

[0085]FIG. 4 is a flowchart showing an operation of the flowmeter ofembodiment 1.

[0086]FIG. 5 is a flowchart showing an operation of the flowmeter ofembodiment 1.

[0087]FIG. 6 is a flowchart showing an operation of a flowmeteraccording to embodiment 2 of the present invention.

[0088]FIG. 7 is a block diagram showing a flowmeter according toembodiment 3 of the present invention.

[0089]FIG. 8 is a flowchart showing an operation of the flowmeter ofembodiment 3.

[0090]FIG. 9 is another flowchart showing an operation of the flowmeterof embodiment 3.

[0091]FIG. 10 is a block diagram showing a flowmeter according toembodiment 4 of the present invention.

[0092]FIG. 11 is a flowchart showing an operation of the flowmeter ofembodiment 4.

[0093]FIG. 12 is a block diagram showing a flowmeter according toembodiment 5 of the present invention.

[0094]FIG. 13 is a block diagram showing a flowmeter according toembodiment 6 of the present invention.

[0095]FIG. 14 is a structure diagram of the flowmeter of embodiment 6.

[0096]FIG. 15 is a timing chart showing an operation of the flowmeter ofembodiment 6.

[0097]FIG. 16 is another timing chart showing an operation of theflowmeter of embodiment 6.

[0098]FIG. 17 is a flowchart showing an operation of the flowmeter ofembodiment 6.

[0099]FIG. 18 is another flowchart showing an operation of the flowmeterof embodiment 6.

[0100]FIG. 19 is another block diagram of the flowmeter of embodiment 6.

[0101]FIG. 20 is a timing chart showing an operation of a flowmeteraccording to embodiment 7 of the present invention.

[0102]FIG. 21 is a flowchart showing an operation of the flowmeteraccording to embodiment 7.

[0103]FIG. 22 is a timing chart showing an operation of a flowmeter ofembodiment 8 of the present invention.

[0104]FIG. 23 is a flowchart showing an operation of the flowmeteraccording to embodiment 8.

[0105]FIG. 24 is a block diagram showing a flowmeter according toembodiment 9 of the present invention.

[0106]FIG. 25 is a timing chart showing an operation of the flowmeteraccording to embodiment 9.

[0107]FIG. 26 is a block diagram showing a flowmeter according toembodiment 10 of the present invention.

[0108]FIG. 27 is a flowchart showing an operation of the flowmeteraccording to embodiment 10.

[0109]FIG. 28 is a timing chart showing an operation of a flowmeter ofembodiment 11 of the present invention.

[0110]FIG. 29 is a timing chart showing an operation of a flowmeter ofembodiment 12 of the present invention.

[0111]FIG. 30 is a timing chart showing an operation of the flowmeter ofembodiment 12.

[0112]FIG. 31 is another timing chart showing an operation of theflowmeter of embodiment 12.

[0113]FIG. 32 is a timing chart showing an operation of a flowmeter ofembodiment 13 of the present invention.

[0114]FIG. 33 is a timing chart showing an operation of a flowmeter ofembodiment 14 of the present invention.

[0115]FIG. 34 is a flowchart showing an operation of a 15 flowmeter ofembodiment 15 of the present invention.

[0116]FIG. 35 is a flowchart showing an operation of a flowmeter ofembodiment 16 of the present invention.

[0117]FIG. 36 is a flowchart showing an operation of a flowmeter ofembodiment 17 of the present invention.

[0118]FIG. 37 is a flowchart showing an operation of a flowmeter ofembodiment 18 of the present invention.

[0119]FIG. 38 is a flowchart showing an operation of a flowmeter ofembodiment 19 of the present invention.

[0120]FIG. 39 is a flowchart showing an operation of a flowmeter ofembodiment 20 of the present invention.

[0121]FIG. 40 is a flowchart showing an operation of a flowmeter ofembodiment 21 of the present invention.

[0122]FIG. 41 is a block diagram showing a flowmeter according toembodiment 22 of the present invention.

[0123]FIG. 42 is a block diagram showing a flowmeter according toembodiment 23 of the present invention.

[0124]FIG. 43 is a flowchart showing an operation of the flowmeteraccording to embodiment 23.

[0125]FIG. 44 is a flowchart showing a digital filter processing of theflowmeter of embodiment 23.

[0126]FIG. 45 is a filter characteristic graph for illustrating anoperation of the flowmeter of embodiment 23.

[0127]FIG. 46 is a flowchart showing an operation of a flowmeter ofembodiment 24 of the present invention.

[0128]FIG. 47 is a flowchart showing an operation of a flowmeter ofembodiment 25 of the present invention.

[0129]FIG. 48 is a flowchart showing an operation of a flowmeter ofembodiment 26 of the present invention.

[0130]FIG. 49 is a flowchart showing an operation of a flowmeter ofembodiment 27 of the present invention.

[0131]FIG. 50 is a flowchart showing an operation of a 30 flowmeter ofembodiment 28 of the present invention.

[0132]FIG. 51 is a block diagram showing a flowmeter according toembodiment 29 of the present invention.

[0133]FIG. 52 is a block diagram showing a flowmeter according toembodiment 30 of the present invention.

[0134]FIG. 53 is a block diagram of periodicity change means of theflowmeter of embodiment 30.

[0135]FIG. 54 is a timing chart for showing a reception detection timingof the flowmeter of embodiment 30.

[0136]FIG. 55 is a block diagram showing a flowmeter according toembodiment 31 of the present invention.

[0137]FIG. 56 is a block diagram of periodicity change means of theflowmeter of embodiment 31.

[0138]FIG. 57A is a block diagram of periodicity change means of theflowmeter of embodiment 32 of the present invention.

[0139]FIG. 57B is a timing chart for showing a reception detectiontiming of the flowmeter of embodiment 32.

[0140]FIG. 58 is a block diagram of periodicity change means of theflowmeter of embodiment 33 of the present invention.

[0141]FIG. 59 is a block diagram of periodicity change means of theflowmeter of embodiment 34 of the present invention.

[0142]FIG. 60 is a block diagram of periodicity change means of theflowmeter of embodiment 35 of the present invention.

[0143]FIG. 61 is a block diagram showing a flowmeter according toembodiment 36 of the present invention.

[0144]FIG. 62 is a diagram showing operations of a first timer and asecond timer according to embodiment 36 of the present invention.

[0145]FIG. 63 is a block diagram showing a flowmeter according toembodiment 37 of the present invention.

[0146]FIG. 64 is a block diagram showing a conventional flowmeter.

[0147]FIG. 65 is a block diagram showing another conventional flowmeter.

[0148]FIG. 66 is a block diagram showing still another conventionalflowmeter.

[0149]FIG. 67 is a flowchart showing an operation of still anotherconventional flowmeter.

[0150]FIG. 68 is a block diagram showing a conventional flowmeter.

DETAILED DESCRIPTION

[0151] Hereinafter, embodiments of the present invention will bedescribed with reference to the drawings.

EMBODIMENT 1

[0152]FIG. 1 is a block diagram showing a flowmeter according toembodiment 1 of the present invention. In FIG. 1, reference numeral 117is first transmission/reception means which is provided in a flow path116 and which functions as transmission/reception means fortransmitting/receiving a signal by using propagation of a sonic wave asa state change in a fluid. Reference numeral 118 is secondtransmission/reception means as transmission/reception means. Referencenumeral 119 is repetition means for repeating signal propagation betweenthe first transmission/reception means 117 and the secondtransmission/reception means 118. Reference numeral 120 is timemeasurement means for measuring a propagation time of a sonic wavepropagated during the repetition in the repetition means 119. Referencenumeral 121 is flow rate detection means for detecting the flow ratebased on a value from the time measurement means 120. Reference numeral122 is number-of-times change means for successively making a change toa predetermined number of repetition times. Furthermore, an elapsed timedetection means 123 for detecting halfway information concerning thepropagation time of propagation repeated in the repetition section 119,frequency detection means 124 for detecting the frequency of a variationin flow rate from the information of the elapsed time detection means123, and number-of-times change means 122 for making a change to asetting such that the measurement time is substantially a multiple ofone cycle of the frequency detected in the frequency detection means124, are included. Herein, data stored in data holding means 125 holdsone propagation time of transmission/reception which has been obtainedby elapsed time detection means 123. The frequency is detected by thefrequency detection means 124 by comparing data held by the data holdingmeans 125 with data of a measured propagation time. Reference numeral126 is switching means for switching operations oftransmission/reception between the first transducer 117 and the secondtransducer 118. Reference numeral 127 is a transmitter for transmittingan ultrasonic signal. Reference numeral 128 is a receiver for receivingan ultrasonic signal.

[0153] Next, an operation and function of the flowmeter are describedwith reference to FIGS. 2 through 5. As shown in FIG. 2, in a flowmeterof the present invention, measurement begins in response to a repetitionstart signal. An input signal is input to the first transducer, and thefirst transducer vibrates to transmit a sonic wave. The sonic wave isreceived by the second transducer. The propagation time of the sonicsignal is measured by the time measurement means based on apredetermined clock count. The delay time in the drawing is a fixedwaiting time which is provided for waiting for attenuation of the soundwave. After detecting a counted value of the delay time and propagationtime as C₁, an input signal is again input to the first transducer totransmit a sonic wave, and the sonic wave is received by the secondtransducer. This repetitive measurement is performed a predeterminednumber of times. The count number received by the second transducer,C_(i)+₁, is compared with the previous count number C_(i), so as todetect the frequency of repetitively occurring flow rate variation. Forexample, as shown in FIG. 3, comparing points V5 and V6 of the flow ratevariation, the difference between the count numbers, C₅-C₆, is anegative value. However, comparing points V6 and V7 of the flow ratevariation, the difference between the count numbers, C₆-C₇, is apositive value. That is, the sign is inverted. Then, again, the timewhen the difference between the count values, C_(i)-C_(i+1), changesfrom a negative value to a positive value is determined for eachrepetition according to the processing shown in the flowchart of FIG. 4,whereby the frequency is detected.

[0154] The flowchart of FIG. 4 shows a flow of frequency detection.Specifically, FIG. 4 shows that one time measurement counter is held forcomparison with the next time measurement counter, whereby a change in aflow rate variation is detected. Furthermore, as shown in FIG. 5, theprocessing 1 and number-of-times change means are performed before everyflow rate measurement. In this way, the frequency is detected, and inthat cycle, measurement of a propagation time is repeatedly performed.Hence, the flow rate is measured without being affected by a variationbecause the measured flow rate is averaged by measuring at an intervalof one cycle of the variation even when there is a variation in theflow. When measurement is performed not only within one cycle but alsoover a plurality of cycles, the flow rate measurement can be performedwith a high accuracy in a more reliable manner.

[0155] The method for detecting the frequency by use of an inversion ofthe sign of the difference between the count values has been described.However, detection of the frequency may be achieved by detecting a pointat which the difference is maximum, or by detecting a point at which acount value nearest to the held count value is counted again. Further,the detection method which utilizes a comparison with one held data hasbeen described. However, the frequency may be detected by using anautocorrelation or frequency analysis method with a plurality of helddata, or by obtaining a difference among a plurality of held data asdescribed above.

[0156] Thus, the flowmeter does not require means for detecting avariation in a flow, i.e., the structure thereof can be simplified. Thefrequency is detected from the halfway information of the timemeasurement means before the flow rate detection is performed such thatthe time for the repetitive measurement is a multiple of one cycle ofthe variation frequency. Therefore, the flow rate measurement can beperformed with a high accuracy in a reliable manner. Time measurementinformation at each moment is held and compared by the data holdingmeans, whereby the frequency can be detected at each occasion.Furthermore, by successively changing the number of repetition times, aninfluence caused due to a change in a variation of a flow can besuppressed, hence a reliable flow rate measurement can be achieved.Still further, the number of repetition times is set so as to be amultiple of one cycle of the variation frequency before the flow ratemeasurement is performed. Thus, a variation in a flow is averaged, andas a result, the flow rate measurement can be performed with a highaccuracy in a reliable manner.

EMBODIMENT 2

[0157]FIG. 6 is a flowchart showing an operation of a flowmeteraccording to embodiment 2 of the present invention. Embodiment 2 isdifferent from embodiment 1 in that the process of embodiment 2 isstructured such that the number of repetition times which is determinedaccording to a frequency obtained by the frequency detection means isused in the next flow rate measurement. The structure of the flowmeterin embodiment 2 is the same as that shown in FIG. 1.

[0158] As shown in FIG. 6, measurement of propagation time T1 of anultrasonic wave propagating from the first transducer is performed,while time measurement information C_(i) of the measurement means atthat time is held in the data holding means. Measurement of propagationtime T2 of an ultrasonic wave propagating from the second transducer isthen performed, and the flow velocity and flow rate are calculated fromtimes T1 and T2. Then, the frequency of a flow variation is detectedfrom the held time measurement information C_(i) by using a methoddescribed in embodiment 1, and the number of repetition times for thenext measurement is changed such that the detected frequency isreflected in the next measurement.

[0159] In this way, the detected frequency of a flow variation is usedin the next measurement, whereby the flow rate measurement and thefrequency can be simultaneously performed. It is not necessary toperform repetitive measurement of sonic wave propagation only fordetecting the variation frequency, and accordingly, the currentconsumption can be decreased. The number of repetition times can be setaccording to the variation frequency, so that the variation is averaged,and the flow rate can be measured with a high accuracy in a reliablemanner.

EMBODIMENT 3

[0160]FIG. 7 is a block diagram of a flowmeter according to embodiment 3of the present invention. Embodiment 3 is different from embodiment 1 inthat the flowmeter of embodiment 3 includes: flow rate variationidentification means 129 to determine the magnitude of a flow ratevariation detected by the flow rate detection means 121; andnumber-of-times change means 122 for changing the number of repetitiontimes such that the flow rate variation identified by the flow ratevariation identification means 129 is decreased, and that the flow ratevariation identification means 129 operates using a standard deviationof the flow rate.

[0161] As shown in the flowchart of FIG. 8, the flow rate Qi is firstmeasured. When the flow rate is equal to or higher than a predeterminedvalue Qm (for example, 100 liter/hour), the number of repetition timesis kept unchanged. When the flow rate is lower than a predeterminedvalue Qm, standard deviation Hi is obtained based on n pieces of databefore the measured flow rate Qi. When the standard deviation Hi isequal to or greater than a predetermined value Hm (for example, 1liter/hour), the number of repetition times is changed. At this time,the number of repetition times is changed (increased) from an initialvalue 10 by a predetermined value dK (for example, two times). When thenumber of repetition times is equal to or greater than a predeterminednumber of times, Km, the number of repetition times is reset to theinitial value and changed again from the first.

[0162] In this way, only when the measured flow rate is lower than apredetermined flow rate, the number of repetition times is changed,whereby the process is stopped when the flow rate is high, andaccordingly, the consumed power is decreased. When the standarddeviation is equal to or greater than a predetermined value, the numberof repetition times is changed such that the flow rate variation becomessmall, whereby the flow rate measurement can be achieved with a highaccuracy in a reliable manner even when there is a variation in a flow.A flow rate variation is identified by using the standard deviation,whereby a variation can be correctly detected. Further, the number ofrepetition times is gradually changed in an incremental manner, wherebythe necessary number of repetition times can be determined because therepetition number can be examined from a small number of times.

[0163] As shown in FIG. 9, only when the measure flow rate is equal toor lower than a predetermined flow rate, and the standard deviation isequal to or higher than a predetermined value, thenumber-of-repetition-times change means operates, so that the number oftimes that the operation of changing the number of times is performed isfurther restricted, and accordingly, the consumed power can bedecreased.

[0164] In the above-described method, the number of times is changed ina gradual incremental manner. However, if the standard deviation whenthe number of times is changed is increased, the number of times may bedecrementally changed. In such a case, when the direction of change ofthe number of times, i.e., increment or decrement, is controlledaccording to a variation of the standard deviation, measurement can beperformed in a more reliable manner. Further, when an electric batterycell is used as the power source of the flowmeter, the consumed power isdecreased, and accordingly, the flowmeter can be used over a long timeperiod.

EMBODIMENT 4

[0165]FIG. 10 is a block diagram of a flowmeter according to embodiment4 of the present invention. Embodiment 4 is different from embodiment 1in that the flowmeter of embodiment 4 includes abnormalityidentification means 130 and flow rate management means 131. The numberof-times change means operates during the execution of processing in theabnormality identification means 130 as predetermined processing andduring the execution of processing in the flow rate management means131.

[0166] As in the flowchart shown in FIG. 11, the number of repetitiontimes is changed during the execution of the processing in theabnormality identification means, and during the execution of processingin the flow rate management means. The number of repetition times can bechanged only when it is necessary, so that the consumed power can bedecreased. That is, in consideration of an urgency of executingabnormality identification, the flow rate should be measured within ashort space of time. In a flow rate measurement method which is executedin accordance with a variation in a flow, abnormality identification isslow. When the number of repetition times is changed in accordance withthe variation frequency before performing measurement, the measurementcan be achieved within a short space of time. Furthermore, the flow ratemanagement is performed for managing what load is used in the downstreamside. It is necessary to detect and identify the flow rate within ashort space of time. Similar to abnormality identification, the numberof repetition times is changed so as to conform to the variationfrequency before performing measurement, whereby the measurement can beachieved within a short space of time.

EMBODIMENT 5

[0167]FIG. 12 is a block diagram of a flowmeter according to embodiment5 of the present invention. Embodiment 5 is different from embodiment 1in that the transmission/reception means utilizes propagation of heatfor detecting a change in the state of fluid. Reference numeral 132denotes a heater for emitting heat, and reference numeral 133 denotes atemperature sensor for receiving the heat.

[0168] Also in the case where the transmission means and the receptionmeans utilize heat, the variation frequency can be detected from thevariation in a heat propagation time, and accordingly, the structure canbe simplified. Further, the times to perform repetitive measurement canbe changed. When the number of repetition times is a multiple of onecycle of the variation frequency, the flow rate measurement can beperformed with a high accuracy in a reliable manner. Furthermore, thenumber of times of successive repetition can be changed according to achange in a flow variation, and an influence of variation can be quicklysuppressed, whereby the flow rate measurement can be performed in areliable manner. Further still, immediately before performing flow ratemeasurement, the number of repetition times is set to a multiple of onecycle of the variation frequency, and accordingly, a variation of a flowis averaged, so that the flow rate measurement can be performed with ahigh accuracy in a reliable manner.

EMBODIMENT 6

[0169]FIG. 13 is a block diagram showing a flowmeter according toembodiment 6 of the present invention. In FIG. 13, reference numeral 223denotes a first piezoelectric transducer, which is first vibration meansof transmission/reception means that is provided in a flow path 224 andthat performs transmission/reception using an ultrasonic wave as a statechange of fluid. Reference numeral 225 denotes a second piezoelectrictransducer, which is second vibration means of transmission/receptionmeans that performs transmission/reception of an ultrasonic wave.Reference numeral 226 denotes a switch (switching means) for switching atransmission/reception operation of the first piezoelectric transducerand the second piezoelectric transducer. Reference numeral 227 denotestime measurement means for measuring by a sing-around method apropagation time of a sonic wave repeatedly transmitted/received betweenthe first piezoelectric transducer 223 and the second piezoelectrictransducer 225. Reference numeral 228 denotes flow rate detection meansfor detecting the flow rate based on a value of the time measurementmeans. Reference numeral 229 denotes variation detection means formeasuring a pressure variation in the flow path by using the firstpiezoelectric transducer 223 and the second piezoelectric transducer225. Reference numeral 230 denotes measurement control means forstarting measurement in synchronization with a timing of the pressurevariation detected by the variation detection means.

[0170] The measurement control means 230 performs measurement controlsuch that measurement of a first measurement time T1 is started at arising edge of an output of the variation detection means 229, andmeasurement of a second measurement time T2 is started at a falling edgeof the output of the variation detection means 229. The measurementcontrol means 230 performs measurement start control such that, for thenext measurement, measurement of a first measurement time T1 isperformed at a falling edge of the output of the variation detectionmeans, and measurement of a second measurement time T2 is performed at arising edge of the output of the variation detection means. The flowrate measurement means 228 calculates the flow rate by successivelyaveraging the first flow rate obtained using the previous firstmeasurement time T1 and the second measurement time T2, whilealternately changing the start of measurement, with the second flow rateobtained using the next first measurement time T1 and the secondmeasurement time T2. Reference numeral 231 denotes a selection switch asselection means for switching between a transmission/reception operationof an ultrasonic wave by using the second piezoelectric transducer and apressure variation detection operation. Reference numeral 232 denotes atransmitter of an ultrasonic signal. Reference numeral 233 denotes areceiver of an ultrasonic signal. Reference numeral 234 denotesrepetition means for performing a sing around measurement. Referencenumeral 235 denotes operation check means for checking the operations ofthe first piezoelectric transducer and the second piezoelectrictransducer.

[0171] Next, an operation and function are described with reference toFIGS. 14 through 19. In a flow path having a structure shown in FIG. 14,propagation time T1 of an ultrasonic wave from the first piezoelectrictransducer 223 to the second piezoelectric transducer 225 is T1=L/(C+Vcos θ). Propagation time T2 of an ultrasonic wave from the secondpiezoelectric transducer 225 to the first piezoelectric transducer 223is T2=L/(C−V cos θ). Herein, V denotes a flow velocity in the flow path,C denotes acoustic velocity, and θ denotes an angle of inclination. Withthe difference of inverse numbers of T1 and T2, the flow velocity V isobtained from T1 and T2 as shown in the following expression:

1/T 1−1/T 2=2V cos θ/L

V=(L/2 cos θ)·(1/T 1−1/T 2)

[0172] If there is a pressure variation in the flow path, the flowvelocity changes according to the pressure variation. Thus, T1 and T2are expressed as follows:

T 1=L/(C+V cos θ+u·sin(2πft))

T 2=L/(C−V cos θ−u·sin(2πft+ψ))

[0173] where f denotes variation frequency, u denotes variation flowvelocity, and ψ denotes a difference between a start time of T1measurement and a start time of T2 measurement (phase difference). Thedifference between the inverse numbers of Ti and T2 is expressed asfollows:

1/T 1−1/T 2=(2V cos θ+u·(sin(2πft)+sin(2πft+ψ)))/L

[0174] When ψ=π, sin(2πft+ψ)=sin(2πft). That is, an influence of thevariation is cancelled. Thus,

V=(L/2 cos θ)·(1/T−1/T 2)

[0175] That is, the flow velocity V can be measured when there is avariation, and the flow rate can be measured in consideration of thecross-sectional area of the flow path. In the above example, themeasurement based on a single transmission/reception operation has beendescribed. However, in the case where the integrated time is obtained bya sing-around method where the propagation time is repeatedly measuredby the repetition means 234, T1 and T2 can be expressed similarly asshown in the following expressions: $\begin{matrix}{{T1} = {\sum\left\lbrack {L/\left( {C + {V\quad \cos \quad \theta} + {{u \cdot \sin}\quad \left( {2\pi \quad {fti}} \right)}} \right)} \right\rbrack}} \\{= {\sum{L/\left( {{\sum\left( {C + {V\quad \cos \quad \theta}} \right)} + {\sum\left( {{u \cdot \sin}\quad \left( {2\pi \quad {fti}} \right)} \right)}} \right)}}} \\{{T2} = {\sum\left\lbrack {L/\left( {C - {V\quad \cos \quad \theta} - {u \cdot {\sin \left( {{2\pi \quad {fti}} + \psi} \right)}}} \right)} \right\rbrack}} \\{= {\sum{L/\left( {{\sum\left( {C + \quad {V\quad \cos \quad \theta}} \right)} + {\sum\left( {{u \cdot \sin}\quad \left( {{2\pi \quad {fti}} + \psi} \right)} \right)}} \right)}}}\end{matrix}$

[0176] where i denotes the number of times of sing-around, and Σ denotesan integration from i=1 to N. The sing-around method is a method wheretransmission/reception of an ultrasonic wave is repeated, whereby a longtotal propagation time is obtained, and accordingly, the measurementaccuracy is increased. Herein, the details of measurement processing ofthe sing-around method are omitted.

[0177] From the difference of the inverse numbers of T1 and T2, thefollowing expression can be obtained:1/T1 − 1/T2 = (∑[2  V  cos   θ] + ∑[u ⋅ (sin (2π  ft)) + ∑[u ⋅ sin (2π  ft + ψ))])/∑L

[0178] When ψ=π, sin(2πft+ψ)=−sin(2πft). That is, an influence of thevariation is cancelled when the sing-around method is used. Thus,

V=(L/2 cos θ)·(1/T 1−1/T 2)

[0179] That is, the flow velocity V can be measured when there is avariation, and the flow rate can be measured in consideration of thecross-sectional area of the flow path.

[0180] The start timing when the time difference ψ is π is describedwith reference with FIG. 15. An output signal of the variation detectionmeans 229 is achieved by comparing and detecting a zero-crossing pointof an alternating component of the pressure variation by a comparator.That is, measurement of T1 is started at a rising edge of the outputsignal of the variation detection means, and integral time T1 ismeasured for a predetermined number of times of sing-around. On theother hand, measurement of T2 is started at a falling edge of the outputsignal of the variation detection means 29, and integral time T2 ismeasured for the same predetermined number of times of sing-around. Asshown in FIG. 15, T1 is measured within zones A, B, and C of thepressure waveform. T2 is measured within zones F, G, and H, which havean inverted amplitude of that within zones A, B, and C. Thus, thepressure variation is cancelled.

[0181] When the pressure variation exhibits a positive-negative(peak-to-peak) symmetry waveform as shown in FIG. 15, the variation canbe cancelled by a single measurement operation for each of T1 and T2.However, when the pressure variation exhibits a positive-negative(peak-to-peak) asymmetry waveform as shown in FIG. 16, the variation canbe cancelled by appropriately changing the time from which themeasurement is started. That is, the measurement of T1 is started at arising edge of the output signal of the variation detection means 229,and integral time T1 is measured for a predetermined number of times ofsing-around. On the other hand, measurement of T2 is started at afalling edge of the output signal of the variation detection means 229,and integral time T2 is measured for the same predetermined number oftimes of sing-around. Then, in the next measurement cycle, themeasurement of T1 is started at a falling edge of the output signal ofthe variation detection means 229, and integral time T1 is measured fora predetermined number of times of sing-around. On the other hand,measurement of T2 is started at a rising edge of the output signal ofthe variation detection means 229, and integral time T2 is measured forthe same predetermined number of times of sing-around. Referring to FIG.16, in the first measurement cycle, T1 is measured within zones A, B,and C, and T2 is measured within zones D, E, and F. After the firstmeasurement cycle, the difference in the measured value between zones Cand F, C−(−F), is left as an error because the waveforms of zones C andF are different. In the second measurement cycle, T1 is measured withinzones H, I, and J which have an opposite waveform, and T2 is measuredwithin zones K, L, and M. After the second measurement cycle also, thedifference in the measured value between zones J and M is left as anerror because the waveforms of zones J and M are different. In thesecond measurement cycle, the measurement is performed for an ultrasonicwave transmitted from the upstream side within zone M, whereas themeasurement is performed for an ultrasonic wave transmitted from thedownstream side within zone 3. Thus, the signs of the measured valuesare inverted. As a result, the difference in the measured value betweenzones J and M, (−J−M), is left as an error. Hence, if considering thatC=M and F=J, when C−(−F) and (−J−M) are added and averaged, a result ofthe operations is zero. That is, the pressure variation is cancelled. Itis apparent that, when the direction in which an ultrasonic wave istransmitted is alternately changed at each measurement, the measurementcan be started with a constant timing. In the above example, themeasurement for two measurement cycles has been described. However, whenthe waveform of the pressure variation is asymmetrical and complicated,measurement is repeated while successively changing the time when themeasurement is started according to the periodicity of a waveform,whereby the measured values are averaged, and accordingly, an error canbe suppressed to a minimum value.

[0182] Next, a flow of the measurement is described with reference tothe flowcharts of FIGS. 17 and 18. In the first step, whether or not thesignal of the variation detection means is at a rising edge isdetermined. When a rising edge is not detected, the determination isrepeated until the rising edge of the output signal of the variationdetection means 229 arrives. If a rising edge does not appear after apredetermined time period, detection of a rising edge is discontinued bydetection cancellation means, and it is determined that there is nopressure variation. Then, measurement of first measurement time T1 andsecond measurement time T2 are performed. When a rising edge isdetected, the first measurement time T1 is measured. Then, whether ornot the signal of the variation detection means 229 is at a falling edgeis determined. When a falling edge is detected, measurement of secondmeasurement time T2 is performed. If a falling edge does not appearafter a predetermined time period, detection of a falling edge isdiscontinued by detection cancellation means, and it is determined thatthere is no pressure variation. Then, measurement of second measurementtime P2 is performed. From the first measurement time T1 and secondmeasurement time T2, the flow rate Q(j) is calculated.

[0183] In the next measurement cycle, as shown in FIG. 18, the processis started with falling-edge detection. After the falling-edge detectionstep is performed, the first measurement time T1 is measured.Thereafter, after the rising-edge detection step is performed, thesecond measurement time T2 is measured. From the first measurement timeT1 and second measurement time T2, the flow rate Q(j+1) is calculated.The measurement is repeated while changing the time at which themeasurement is started, and the first flow rate Q(j) and second flowrate Q(j+1) are measured and successively averaged, whereby the flowrate Q is calculated. Thus, the measure values are averaged, whereby anerror can be removed in principle.

[0184] Since a pressure variation in the flow path can be measured withthe second piezoelectric transducer 225, it is necessary to provide apressure sensor. Thus, the size of a flowmeter can be decreased, and thestructure of the flow path can be simplified. Further, the flow rate canbe instantaneously measured with a high accuracy in a reliable mannereven when a pressure variation occurs. The measurement is performed whena change in the pressure variation is inverted, whereby the phases ofthe pressure variation and the measurement timing can be shifted. Thus,a measurement error caused, due to the pressure variation can be offset.Furthermore, at each measurement, the timing at which the measurement isperformed is alternately changed between a positive point and a negativepoint, whereby an influence of the pressure variation can be offset evenwhen the pressure variation is asymmetrical between the high pressureside and the low pressure side. Furthermore, the measurement is repeatedaccording to the sing-around method, whereby the measured values can beaveraged within a single measurement cycle. Therefore, the flow ratemeasurement can be performed in a reliable manner. Furthermore, by theselection means, at least one of the first and second vibration meanscan be selected and used for pressure detection. Thus, both the flowrate measurement and the pressure measurement can be achieved. Avariation is detected at a point in the vicinity where a pressurevariation is zero, whereby the frequency of the variation can becorrectly grasped, and the flow rate can be offset. Even when there isno variation, the flow rate can be automatically measured at apredetermined time. The piezoelectric transducers are used together withthe variation detection means. Therefore, an ultrasonic wave is used fordetecting a pressure variation while being used fortransmission/reception. Moreover, it is not necessary to secure a placefor installing pressure detection means which is exclusively used forpressure detection, and the number of parts which can cause leakage offluid can be decreased.

[0185] It should be noted that, even when the detection of a pressurevariation which has been described in this embodiment is performed withpressure detection means which is exclusively used for pressuredetection, the same functional effects can be obtained. The examplewhere the second piezoelectric transducers provided on the downstreamside is used for pressure detection has been described. However, evenwhen the first piezoelectric transducers provided on the upstream sideis used for pressure detection, the same effects can be obtained.Further, even when the first piezoelectric transducers on the upstreamside and the second piezoelectric transducers on the downstream side arealternately used for pressure detection as shown in FIG. 19, the sameeffects can be obtained. Moreover, by alternately using thepiezoelectric transducers, the operation state of each piezoelectrictransducer can be checked. That is, when the variation detection meansdetects the same signal frequency from both piezoelectric transducers,it can be determined that the both piezoelectric transducers areoperating normally.

[0186] In the above-described example, the flowmeter is ageneral-purpose measuring device. However, when a flowmeter of thepresent invention is used in a gas meter, the flow meter can be providedin a pipeline in which fluctuation occurs, such as a pipeline systemwhere a gas engine heat pump is used. Furthermore, this embodiment hasbeen described in conjunction with a pressure variation. However, it isapparent that the same effects can be obtained for a flow ratevariation.

EMBODIMENT 7

[0187]FIG. 20 is a timing chart showing an operation of a flowmeteraccording to embodiment 7 of the present invention. Embodiment 7 isdifferent from embodiment 6 in that the flowmeter of embodiment 7includes repetition means 234 for performing signaltransmission/reception based on a sing-around method a plurality oftimes over a period which is a multiple of one cycle of a variationfrequency. The structure of the flowmeter of embodiment 7 is shown inFIG. 13.

[0188] In an example illustrated in FIG. 21, measurement is started withan interval of a predetermined time period (e.g., 2 seconds). When apredetermined time arrives, the frequency of a variation is measured anddetected by the variation detection means 229. Then, the number of timesof a sing-around process is set so as to substantially conform with thevariation frequency. For example, the time spent for a singlepropagation can be calculated by dividing the distance between thepiezoelectric transducers, which transmit/receive an ultrasonic wave, bythe velocity of sound. A required number of times of the sing-aroundprocess can be calculated by dividing the measured frequency by thecalculated time spent for a single propagation. The measurement of theflow rate is repeated based on the number of times of the sing-aroundprocess. At step 7 in FIG. 21, the process 7 of FIG. 17 is performed.

[0189] In this way, the number of times of the sing-around process ischanged so as to conform with a variation frequency, whereby one cycleof the variation frequency can be measured. Accordingly, the pressurevariation can be averaged, and the flow rate can be measured in areliable manner. The measurement is performed while the pressuresynchronization and the number of times of the sing-around processconform with a multiple of one cycle of the variation frequency, wherebythe flow rate measurement can be performed in a further reliable manner.Furthermore, since the pressure synchronization can be detected byutilizing a signal of the piezoelectric transducers, a synergisticeffect can be obtained, i.e., the variation frequency can be detected,and the flow rate measurement can be performed in a reliable manner.

[0190] In FIG. 20, the measurement for two cycles has been described.However, when the propagation distance is short, in order to increasethe accuracy of the measurement, it is necessary to perform asing-around process for more than a predetermined number of times.Therefore, when the number of times of the sing-around process which isobtained from the variation frequency is smaller than the predeterminednumber of times, the number of times of the sing-around process isdetermined so as to be a multiple of the variation frequency.

EMBODIMENT 8

[0191]FIG. 22 is a timing chart showing an operation of a flowmeteraccording to embodiment 8 of the present invention. Embodiment 8 isdifferent from embodiment 6 in that a flowmeter of embodiment 8 includesrepetition means 234 for performing measurement of atransmitted/received sonic wave such that, when an output of thevariation detection means 229 makes a predetermined change (e.g., whenthe output falls), measurement of a transmitted/received sonic wave isstarted, and sing-around process is repeated until the output of thevariation detection means makes a predetermined change (e.g., when theoutput falls). The flow meter of embodiment 8 has the structure shown inFIG. 13.

[0192] As shown in FIG. 23, a rising edge of a variation detectionsignal is detected at the start of the measurement, and the sing-aroundprocess is started. Then, when the variation detection signal risesagain, the sing-around process is stopped, and a first measurement timeT1 is measured. Next, a falling edge of the variation detection signalis detected at the start of the measurement, and the sing-around processis started. Then, when the variation detection signal falls again, thesing-around process is stopped, and a second measurement time T2 ismeasured. From the measurement times T1 and T2, the flow rate iscalculated.

[0193] In this way, the start and stop of the measurement can beconformed with the frequency of the pressure variation, and therefore,the measurement can be performed based on the variation frequency. Thus,the pressure variation is averaged, and the flow rate can be measured ina reliable manner.

EMBODIMENT 9

[0194]FIG. 24 shows a structure of a flowmeter according to embodiment 9of the present invention. Embodiment 9 is different from embodiment 6 inthat the flowmeter of embodiment 9 includes: two-bit count means 236 forcounting a variation of an output signal of the variation detectionmeans 229; and flow rate detection means 228 where measurement isperformed such that a count value of the count means 236 is differentbetween the first time measurement and the second time measurement, andthe flow rate measurement is performed only when all the combinations ofthe two bits are achieved for the same number of times. The timing chartof the measurement is shown in FIG. 25.

[0195] As shown in FIG. 25, when a variation is repeated by units of twocycles, for example, measurement of T1 is started at a time when anoutput of the count means is (1,0), and an output of the variationdetection means is at a rising edge. Measurement of T2 is started at asubsequent falling edge of the variation detection means. Suchmeasurement can be notionally expressed as Q(i)=(A−B+C)−(−B+C−D)=A+D. Inthe next measurement cycle, measurement of T1 is started at a time whenan output of the count means is (1,1) and at a falling edge of thevariation detection means. Measurement of T2 is started at a subsequentrising edge of the variation detection means. Such measurement can benotionally expressed as Q(i+1)=(−B+C−D)−(C−D+A)=−A−B. Subsequentmeasurement can be notionally expressed as: Q(i+2)=(C−D+A)−(−D+A−B)=C+B;and Q(i+3)=(−D+A−B)−(A−B+C)=−C−D. Thus, Q(i)+Q(i+1)+Q(i+2)+Q(i+3)=0.That is, a pressure variation is cancelled.

[0196] In the above example, the measurement for four measurement cycleshas been described. However, when the waveform of the pressure variationis asymmetrical and complicated, measurement is repeated whilesuccessively changing the time when the measurement is started accordingto the periodicity of a waveform, whereby the measured values areaveraged, and accordingly, an error can be suppressed to a minimumvalue. Since the measurement can be performed at all the variationtimings, averaging of the measured values is achieved, and the flow ratecan be measured in a reliable manner.

EMBODIMENT 10

[0197]FIG. 26 shows a structure of a flowmeter according to embodiment10 of the present invention. Embodiment 10 is different from embodiment6 in that the flowmeter of embodiment 10 includes: frequency detectionmeans 237 for detecting the frequency of a signal of the variationdetection means 229; and measurement control means 230 for startingmeasurement only when the frequency detected by the frequency detectionmeans 237 is equal to a predetermined frequency.

[0198] As shown in FIG. 27, the measurement is started only when thesignal of the variation detection means 229 is equal to a predeterminedfrequency Tm. With such an arrangement, the measurement can be performedat a predetermined variation frequency even when the frequency varies.Even with a pressure waveform shown in FIG. 25, the flow rate can bemeasured only for a specific pressure variation so long as the frequencyis detected. Thus, even when the frequency of the pressure variationvaries, the flow rate can be measured within a short space of time in areliable manner. The frequency is detected at a time interval (e.g., 2milliseconds), whereby flexibility is given to the measurement, so thatthe measurement can be continued without interruption.

EMBODIMENT 11

[0199]FIG. 28 shows a structure of a flowmeter according to embodiment11 of the present invention. Embodiment 11 is different from embodiment6 in that the transmission/reception means utilizes propagation of heatfor detecting a change in the state of fluid. Reference numeral 238denotes a heater for emitting heat, reference numeral 239 denotes afirst temperature sensor for receiving the heat, and reference numeral240 denotes a second temperature sensor for receiving the heat. Thesecond temperature sensor 240 itself can generate heat and detect achange in the state of fluid based on a change in its own resistancevalue.

[0200] Of course, the second temperature sensor is also used as heattransmission/reception means, whereby a change in the state of fluid,i.e., a variation of the flow velocity, or a variation of pressure, canbe detected. Furthermore, the measurement for one measurement cycle isperformed in synchronization with the detected variation. Therefore, theflow rate measurement can be performed with a high accuracy in areliable manner similarly as described in previous embodiments.

EMBODIMENT 12

[0201]FIG. 29 is a block diagram showing a flowmeter according toembodiment 12 of the present invention. In FIG. 29, reference numeral323 denotes a first piezoelectric transducer, which is first vibrationmeans of transmission/reception means that is provided in a flow path324 and that performs transmission/reception using an ultrasonic wave asa state change of fluid. Reference numeral 325 denotes a secondpiezoelectric transducer, which is second vibration means oftransmission/reception means that performs transmission/reception of anultrasonic wave. Reference numeral 326 denotes a switch (switchingmeans) for switching a transmission/reception operation of the firstpiezoelectric transducer and the second piezoelectric transducer.Reference numeral 327 denotes time measurement means for measuring apropagation time of a sonic wave repeatedly transmitted/received betweenthe first piezoelectric transducer 323 and the second piezoelectrictransducer 325. Reference numeral 328 denotes flow rate detection meansfor detecting the flow rate based on a value of the time measurementmeans. Reference numeral 329 denotes pressure variation detector whichfunctions as variation detection means for detecting a pressurevariation in the flow path 324. Reference numeral 330 denotessynchronization pulse output means which functions as variationdetection means for converting a pressure signal of the pressurevariation detector 329 to a digital signal. Reference numeral 331denotes measurement control means for directing measurement so as to bein synchronization with a timing of the pressure variation detected bythe variation detected means. Reference numeral 332 denotes atransmitter for the transmission/reception means of an ultrasonicsignal. Reference numeral 333 denotes a receiver for thetransmission/reception means of an ultrasonic signal. Reference numeral334 denotes repetition means for repeating transmission/reception of anultrasonic wave. Reference numeral 335 denotes measurement monitoringmeans for monitoring abnormality of the measurement control means.

[0202] Next, an operation and function are described with reference toFIGS. 14, 30, and 31. In a flow path having a structure shown in FIG.14, propagation time T1 of an ultrasonic wave from the firstpiezoelectric transducer 323 to the second piezoelectric transducer 325is T1=L/(C+V cos θ). Propagation time T2 of an ultrasonic wave from thesecond piezoelectric transducer 325 to the first piezoelectrictransducer 323 is T2 =L/(C−V cos θ). Herein, V denotes a flow velocityin the flow path, C denotes acoustic velocity, and θ denotes an angle ofinclination. With the difference of inverse numbers of T1 and T2, theflow velocity V is obtained from T1 and T2, by changing the aboveexpressions, as shown in the following expression:

V=(L/2 cos θ) (1/T 1−1/T 2)

[0203] If there is a pressure variation in the flow path, the flowvelocity changes according to the pressure variation. Thus, T1 and T2are expressed as follows:

T 1=L/(C+V cos θ+u·sin(2πft))

T 2=L/(C−V cos θ−u·sin(2πft+ψ))

[0204] where f denotes variation frequency of pressure, u denotesvariation flow velocity, and ψ denotes difference between a start timeof T1 measurement and a start time of T2 measurement (phase difference).The difference between the inverse numbers of T1 and T2 is expressed asfollows:

1/T 1−1/T 2=(2V cos θ+u·(sin(2πft)+sin(2πft+ψ)))/L

[0205] When ψ=π, sin(2πft+ψ)=−sin(2πft). That is, an influence of thevariation is cancelled. Thus,

V(L/2 cos θ)·(1/T 1−1/T 2)

[0206] That is, the flow velocity V can be measured when there is avariation, and the flow rate can be measured in consideration of thecross-sectional area of the flow path. Thus, when ψ=π, the measurementcontrol means, which measures the flow rate while detecting a pressurevariation, can measure the flow rate with a high accuracy in a reliablemanner without being influenced by a pressure variation. In the aboveexample, the measurement based on a single transmission/receptionoperation has been described. However, it is apparent that, also in thecase where the integrated time is obtained by a method where thepropagation time is repeatedly measured by the repetition means 234,flow rate can be similarly obtained.

[0207] As shown in FIG. 30, the measurement control means 331 outputs ameasurement start signal when a predetermined measurement time arrives(e.g., every two seconds), and waits for a change in an output signal ofthe synchronization pulse output means whose threshold value is azero-crossing point of a pressure variation. Then, when a falling signalof an output signal of the synchronization pulse output means 330 isoutput as the first output signal, measurement of first measurement timeT1 is started, and measurement of a propagation time is repeated until arising signal of the output signal of the synchronization pulse outputmeans 330 is output as the second output signal. In the next measurementcycle, measurement of second measurement time T2 is started when arising signal of the output signal of the synchronization pulse outputmeans 330 is output as the first output signal, and measurement of apropagation time is repeated until a falling signal of the output signalof the synchronization pulse output means 330 is output as the secondoutput signal. Then, the measurement times T1 and T2 obtained by thetime measurement means 327 is converted into the flow rate by the flowrate detection means 328, and the flow rate measurement is completed.

[0208] As shown in FIG. 31, the measurement control means 331 outputs ameasurement start signal when a predetermined measurement time arrives.However, when no change occurs in the output signal of thesynchronization pulse output means 330 after a predetermined timeperiod, the measurement control means 331 automatically outputs ameasurement start signal, and measurement is performed according to apredetermined number of repetition times (e.g., 256 times). For example,in the case where measurement is performed at an interval of 2 seconds,and a pressure variation occurs within a range from 10 Hz to 20 Hz, thepredetermined period as a waiting time can be set within a range from0.1 second to 2 seconds. However, in this case, it is preferable toselect 1 second as an optimum value. Furthermore, the predeterminednumber of repetition times can be set within a range from 2 times to 512times. However, in this case, it is preferable to select an optimumvalue according to the frequency of a pressure variation.

[0209] Thus, even when no variation occurs in pressure after ameasurement start signal is output, the measurement is started after apredetermined period, whereby the flow rate measurement can be surelyperformed when it is necessary to perform the flow rate measurement. Forexample, in a flowmeter of a gas meter, whether or not there is a gasflow is measured when an earthquake occurs. Even when the flowmeter iswaiting for occurrence of a pressure variation when the earthquakeoccurs, and a synchronization pulse output signal cannot be obtained dueto abnormality in a pressure variation, the flow rate measurement can beautomatically performed, and therefore, any abnormality can be dealtwith.

[0210] In the above example, a variation in a flow has been described asa pressure variation in the flow path. However, it is apparent that thesame effects can be obtained by using flow velocity variation detectionmeans even when there is a variation in the flow velocity.

EMBODIMENT 13

[0211]FIG. 32 is a timing chart showing an operation of a flowmeteraccording to embodiment 13 of the present invention. Embodiment 13 isdifferent from embodiment 12 in that the flowmeter of embodiment 13includes measurement monitoring means 335 wherein, when a start signalis not issued within a predetermined period after a direction from themeasurement control means 331 is issued, measurement is not performeduntil a next direction from the measurement control means is issued. Thestructure of the flowmeter of embodiment 13 is shown in FIG. 29.

[0212] As shown in FIG. 32, the measurement control means 331 outputs ameasurement start signal when a predetermined measurement time arrives.However, when no change occurs in the output signal of thesynchronization pulse output means after waiting for such a change for apredetermined time period, the measurement monitoring means 335 directsthe measurement control means 331 to stop waiting for a change in thesynchronization pulse signal. The measurement control means 331 waitsfor a next measurement time (e.g., 2 seconds later). Herein, ifmeasurement is performed at an interval of 2 seconds, and a pressurevariation occurs within a range from 10 Hz to 20 Hz, the predeterminedperiod as a waiting time can be set within a range from 0.1 second to 2seconds. However, in this case, it is preferable to select 1 second asan optimum value.

[0213] As described above, when no change occurs in the pressure after ameasurement, start signal is issued, waiting for a change is stoppedafter a predetermined time period has elapsed, and flow rate measurementis not performed, whereby a low-accuracy measurement of flow rate can beavoided. In FIG. 32, a time when the first propagation time T1 ismeasured is shown. However, if a synchronization pulse does not occurwhen the second propagation time T2 is measured, an interval between thetime when T1 is measured and the time when T2 is measured becomesconsiderably long, and accordingly, the measurement accuracy decreases.Such measurement with a decreased accuracy can be avoided. Furthermore,since the measurement operation is suspended until a next measurementdirection is issued, unnecessary measurement is avoided, and consumedpower can be reduced. For example, in a gas meter where a microcomputerfor controlling a safety function is driven by an electric battery cell,the consumed power is reduced, and accordingly, a long lifetime can beobtained.

EMBODIMENT 14

[0214]FIG. 33 is a timing chart showing an operation of a flowmeteraccording to embodiment 14 of the present invention. Embodiment 14 isdifferent from embodiment 12 in that the flowmeter of embodiment 14includes measurement monitoring means 335 wherein, when an end signal isnot issued within a predetermined period after a start signal is issued,reception of a sonic wave is ended, and a start signal is output again.The structure of the flowmeter of embodiment 14 is shown in FIG. 29.

[0215] As shown in FIG. 33, the measurement control means 331 outputs ameasurement start signal when a predetermined measurement time arrives,and detects a first output signal at a falling edge of an output signalof the synchronization pulse output means so as to start measurement.Then, when a second output signal (falling edge) of the output signal ofthe synchronization pulse output means does not emerge after apredetermined time period, waiting for the synchronization pulse signalis ended, and a start signal is output again for measurement. Herein, ifmeasurement is performed at an interval of 2 seconds, and a pressurevariation occurs within a range from 10 Hz to 20 Hz, the predeterminedperiod as a waiting time can be set within a range from 0.1 second to 2seconds. However, in this case, it is preferable to select 1 second asan optimum value. With I second, even if measurement is performed again(re-measurement), the measurement can be completed before a nextmeasurement time arrives after 2 seconds. If no second output signalemerges in the re-measurement process, the operation waits for a nextmeasurement time.

[0216] As described above, when no change occurs in the pressure after ameasurement is started, waiting for a change is ended after apredetermined time period, and flow rate measurement is not performed,whereby an incorrect measurement of flow rate can be avoided.Furthermore, due to re-measurement, lack of certain periodic measurementdata can be prevented, and measurement processing, such as averaging,can be smoothly performed, whereby the accuracy of a measured flow ratevalue can be improved. Furthermore, without a direction concerning theend of measurement, the time measurement means performs erroneousmeasurement, and the measurement accuracy decreases. Such measurementwith a decreased accuracy can be avoided. Furthermore, the measurementis forcibly ended, whereby the measurement process does not stop due toa wait for an end direction. Thus, the process can proceed to asubsequent step. Therefore, a measurement operation can be achieved in areliable manner.

EMBODIMENT 15

[0217]FIG. 34 is a flowchart showing an operation of a flowmeteraccording to embodiment 15 of the present invention. Embodiment 15 isdifferent from embodiment 12 in that the flowmeter of embodiment 15includes measurement monitoring means 335 wherein, when an end signal isnot issued within a predetermined period T after a start signal isissued, reception of a sonic wave is ended, and measured data isabandoned. The structure of the flowmeter of embodiment 15 is shown inFIG. 29.

[0218] As shown in FIG. 34, after a first output signal is output, whena second output signal which indicates the end of one cycle is notissued after the predetermined time T (e.g., 0.5 second) has elapsed,repetition of transmission/reception of a ultrasonic wave is ended, andpreviously measured data are abandoned. Then, after being suspended fora predetermined time period, measurement is resumed.

[0219] As described above, when the measurement is not successful, themeasured data is abandoned, whereby only data measured with a highaccuracy can be used, and a measurement operation can be performed in areliable manner. Further, it is not necessary to hold measured data, andaccordingly, the amount of power consumed for measurement can bedecreased. Furthermore, by monitoring whether or not the predeterminedtime T is longer than a periodical measurement cycle (e.g, 2 seconds),measurement can be performed such that measurement times do not overlapwith each other. Even when a propagation time of an ultrasonic wave isvaried due to a variation of temperature, the measurement operation canbe managed by controlling the same predetermined time T.

EMBODIMENT 16

[0220]FIG. 35 is a flowchart showing an operation of a flowmeteraccording to embodiment 16 of the present invention. Embodiment 16 isdifferent from embodiment 12 in that the flowmeter of embodiment 16includes measurement monitoring means 335 wherein, when the number ofrepetition times is equal to or more than a predetermined number oftimes N1, reception of a sonic wave is ended, and measured data isabandoned. The structure of the flowmeter of embodiment 16 is shown inFIG. 29.

[0221] As shown in FIG. 35, after a first output signal is output, if asecond output signal which indicates the end of one cycle is not issuedwhen transmission/reception of an ultrasonic wave is repeated for thepredetermined number of times N1 (e.g., 512 times) or more, repetitionof transmission/reception of the ultrasonic wave is ended, andpreviously measured data are abandoned. Then, after being suspended fora predetermined time period, measurement is resumed.

[0222] As described above, when the measurement is not successful, themeasured data is abandoned, whereby only data measured with a highaccuracy can be used, and a measurement operation can be performed in areliable manner. Further, it is not necessary to hold measured data, andaccordingly, the amount of power consumed for measurement can bedecreased. Furthermore, even when a propagation time of an ultrasonicwave is varied due to a variation of temperature, the measurement can beperformed independently of the propagation time until the limit of thenumber of repetition times by controlling the number of repetitiontimes.

EMBODIMENT 17

[0223]FIG. 36 is a flowchart showing an operation of a flowmeteraccording to embodiment 17 of the present invention. Embodiment 17 isdifferent from embodiment 12 in that the flowmeter of embodiment 17includes measurement monitoring means 335 wherein, when the number ofrepetition times is equal to or less than a predetermined number oftimes N2, measured data is abandoned, and a start signal is outputagain. The structure of the flowmeter of embodiment 17 is shown in FIG.29.

[0224] As shown in FIG. 36, in predetermined measurement which isperformed based on a variation frequency, when the number of repetitiontimes is equal to or less than a predetermined number of times N2 (e.g.,100 times), previously measured data is abandoned. Then, after beingsuspended for a predetermined time period, the measurement is resumed.

[0225] Even when the measurement is correctly performed, if the numberof repetition times is equal to or less than a predetermined number oftimes, it is probable that a pressure variation is not correctlygrasped. In such a case, obtained data is abandoned and measurement isperformed again, which is possible because the measurement is performedover more than one cycle. Therefore, a measurement operation can beperformed in a reliable manner. Further, it is not necessary to holdmeasured data, and accordingly, the amount of power consumed formeasurement can be decreased.

EMBODIMENT 18

[0226]FIG. 37 is a flowchart showing an operation of a flowmeteraccording to embodiment 18 of the present invention. Embodiment 18 isdifferent from embodiment 12 in that the flowmeter of embodiment 18includes measurement monitoring means 335 wherein, when the number ofrepetition times is equal to or less than a predetermined number oftimes N2, measured data is abandoned, and a start signal is outputagain. The synchronization pulse output means 330 which functions asvariation detection means outputs a second output signal when a signalof the synchronization pulse output means 330 reaches a second cycle andcontinues the measurement until an end signal, indicating the end of thesecond cycle, is issued. The structure of the flowmeter of embodiment 18is shown in FIG. 29.

[0227] As shown in FIG. 37, in predetermined measurement which isperformed based on a variation frequency, when the number of repetitiontimes is equal to or less than a predetermined number of times N2 (e.g.,100 times), previously measured data is abandoned. Then, after beingsuspended for a predetermined time period, a second output signal isoutput when a signal of the synchronization pulse output means 330reaches a second cycle, and the measurement is resumed and continueduntil an end signal of the second cycle is issued.

[0228] Even when the measurement is correctly performed, if the numberof repetition times is equal to or less than a predetermined number oftimes, it is probable that a pressure variation is not correctlygrasped. In such a case, obtained data is abandoned and measurement isperformed again, which is possible because the measurement is performedover more than one cycle. Therefore, a measurement operation can beperformed in a reliable manner. Further, since re-measurement isperformed over two cycles, the measurement accuracy is improved due tosuch a long-time measurement.

EMBODIMENT 19

[0229]FIG. 38 is a flowchart showing an operation of a flowmeteraccording to embodiment 19 of the present invention. Embodiment 19 isdifferent from embodiment 12 in that the flowmeter of embodiment 19includes measurement monitoring means 335 wherein, when the differencebetween the first number of repetition times N3 of measurement, where anultrasonic wave is transmitted from the first transmission/receptionmeans among a pair of transmission/reception means to the secondtransmission/reception means, and the second number of repetition timesN4 of measurement where an ultrasonic wave is transmitted from thesecond transmission/reception means to the first transmission/receptionmeans, is equal to or more than a predetermined number of times, a startsignal is output again. The structure of the flowmeter of embodiment 19is shown in FIG. 29.

[0230] As shown in FIG. 38, in predetermined measurement which isperformed based on a variation frequency, when the difference betweenthe first number of repetition times N3 and the second number ofrepetition times N4 is equal to or more than a predetermined number oftimes M (e.g., 10 times), previously measured data is abandoned. Then,after being suspended for a predetermined time period, the measurementis resumed.

[0231] Even when the measurement is correctly performed, if thedifference between the first number of repetition times N3 and thesecond number of repetition times N4 is large, it is probable that apressure variation is not correctly grasped, or that the frequency of apressure variation is changed. If so, a result of the measurement is notcorrect. Thus, the obtained data is abandoned, and measurement isperformed again, whereby a measurement operation can be performed in areliable manner.

EMBODIMENT 20

[0232]FIG. 39 is a flowchart showing an operation of a flowmeteraccording to embodiment 20 of the present invention. Embodiment 20 isdifferent from embodiment 12 in that the flowmeter of embodiment 20includes repetition means 334 for setting the number of repetition timessuch that the first number of repetition times N3 of measurement, wherean ultrasonic wave is transmitted from the first transmission/receptionmeans among a pair of transmission/reception means to the secondtransmission/reception means, is equal to the second number ofrepetition times N4 of measurement, where an ultrasonic wave istransmitted from the second transmission/reception means to the firsttransmission/reception means. The structure of the flowmeter ofembodiment 20 is shown in FIG. 29.

[0233] As shown in FIG. 39, in predetermined measurement which isperformed based on a variation frequency, measurement is performed forthe second number of repetition times which is equal to the first numberof repetition times N3. That is, the second measurement is performed forthe first number of repetition times N3, whereby the measurement can beperformed without causing a large difference between a true value and ameasured value even when the frequency of a pressure variation variessharply.

[0234] Thus, even when the frequency of a pressure variation sharplyvaries, flow rate measurement can be performed. For example, in the caseof a gas meter, there is a time when it is necessary to perform flowrate measurement for securing safety. Even when the frequency of apressure variation sharply varies, measurement is performed as describedabove, whereby it can be quickly determined whether or not the measuredvalue is in the vicinity of a predetermined flow rate.

EMBODIMENT 21

[0235]FIG. 40 is a flowchart showing an operation of a flowmeteraccording to embodiment 21 of the present invention. Embodiment 21 isdifferent from embodiment 12 in that the flowmeter of embodiment 21includes measurement monitoring means 335 for monitoring a measurementoperation such that the number of times that a start signal is outputagain is limited to a predetermined number of times C so as not topermanently repeat outputting of the start signal. The structure of theflowmeter of embodiment 21 is shown in FIG. 29.

[0236] As shown in FIG. 40, when measurement is performed again aftermeasurement based on a pressure variation has failed, the number oftimes C for the re-measurement is limited (e.g., up to 2 times), wherebyoutputting of the start signal is prevented from being repeatedpermanently. As a result, the flow rate measurement can be performed ina reliable manner.

EMBODIMENT 22

[0237]FIG. 41 is a block diagram showing a flowmeter according toembodiment 22 of the present invention. Embodiment 22 is different fromembodiment 12 in that, in embodiment 22, propagation of heat is utilizedfor detecting a change in the state of fluid. Reference numeral 336denotes a heater for emitting heat. Reference numeral 337 denotes atemperature sensor for receiving the heat.

[0238] Even when a temperature sensor which is heattransmission/reception means is used, flow rate measurement can becontinuously performed with a high accuracy similarly to theabove-described embodiments, because the measurement monitoring meansdetects each abnormality and perform various processing according to thedetected abnormality.

EMBODIMENT 23

[0239]FIG. 42 is a block diagram showing a flowmeter according toembodiment 23 of the present invention. In FIG. 42, reference numeral415 denotes ultrasonic wave flow rate detection means for detecting aninstantaneous flow rate; reference numeral 416 denotes fluctuationdetermination means for determining whether or not the flow rate valuevaries in a pulsed manner; reference numeral 417 denotes stable flowrate calculation means for calculating a flow rate value by usingdifferent means according to the determination result of the fluctuationdetermination means; and reference numeral 418 denotes filter processingmeans for performing digital filter processing on a flow rate value.

[0240] Next, an operation and function are described with reference toFIGS. 43 through 45. As shown in FIG. 43, in the flowmeter of thepresent invention, when the difference between an instantaneous flowrate Q(i) measured by the ultrasonic wave flow rate detection means anda previously-measured instantaneous flow rate Q(i−1) is equal to orgreater than a predetermined value (e.g., 1 liter/hour), the fluctuationdetermination means determines that there is a pulse. When there is apulse, the filter coefficient for filter processing is changed accordingto the magnitude of the pulse. When there is no pulse, the filterprocessing is not performed, and the instantaneous flow rate value istreated as a stable flow rate. Herein, the digital filter processing isperformed based on the flow shown in FIG. 3 and is expressed, forexample, as the following expression: D(i)=α(D(i−α)Q(i), where α denotesthe filter coefficient, Q(i) denotes i-th instantaneous flow rate, andD(i) denotes a stable flow rate to be obtained after the filterprocessing. Such a filter has a characteristic of a low-pass filterwhich is shown in FIG. 45. As the filter coefficient is closer to 1(generally, 0.999), the filter allows only a lower frequency componentto pass therethrough. Thus, the filter can remove a varying value so asnot to pass through the filter. When the variation amplitude is small,filter coefficient α2 (generally, α2=0.9) is selected, and an improvedresponse characteristic to a flow rate variation is obtained with such arelaxed filter characteristic, so that a flow rate variation can bequickly dealt with. Further, when the variation amplitude is large,filter coefficient al (generally, α2=0.9999) is selected, and avariation in a flow rate value is suppressed with such an extreme lowpass filter characteristic.

[0241] Furthermore, a pulse component A(i) can be obtained byexpression, A(i)=Q(i)−D(i), and A(i) can be used as a variationamplitude.

[0242] Thus, the filter processing is performed when the amplitude of apulse is equal to or greater than a predetermined value, whereby avariation component can be removed. Accordingly, even when a pulseoccurs, stable flow rate measurement can be performed with oneultrasonic wave flow rate measurement means. Further, a calculationequivalent to averaging processing can be performed by filter processingwithout using a large number of memories for storing data. Moreover, thefilter characteristic can be freely modified by changing one variable,i.e., a filter coefficient α. Thus, the filter characteristic can bemodified according to the magnitude of a pulse. Furthermore, when apulse occurs, a sharp filter characteristic is selected so as to rendera large pulse stable, and the filter processing can be performed onlywhen a pulse occurs. Furthermore, the determination is performed basedon the variation amplitude of a pulse, whereby the filter processing canbe modified based on the variation amplitude of a pulse. Furthermore,since the filter characteristic is modified based on the variationamplitude, a relaxed filter characteristic that allows a quick variationaccording to a variation in a flow rate is selected when the variationis small, and when the variation is large, a sharp filter characteristicis selected such that a variation of the flow rate due to a pulse issignificantly suppressed.

[0243] In this embodiment, the digital filter processing methoddescribed is as shown in FIG. 44. However, the same effects can beobtained by using other filter processing method.

[0244] In the above-described example, the flowmeter is ageneral-purpose measuring device. However, when the flowmeter of thisembodiment is used in a gas meter, the flow meter can be provided to aflow-path pipe in which fluctuation occurs, such as a pipeline systemwhere a gas engine heat pump is used.

EMBODIMENT 24

[0245]FIG. 46 is a flowchart showing an operation of a flowmeteraccording to embodiment 24 of the present invention. Embodiment 24 isdifferent from embodiment 23 in that the flowmeter of embodiment 24includes pulse amplitude detection means for detecting the variationamplitude of a pulse based on two flow rate values which have beensubjected to filter processing while changing the filter coefficient α.

[0246] As shown in FIG. 46, the difference between a first flow ratevalue which has been subjected to filter processing with a filtercoefficient al (e.g., α1=0.999) and a second flow rate value which hasbeen subjected to filter processing with a filter coefficient α2(e.g.,α2=0.9) is greater than a predetermined value (e.g., 1 liter/hour), thelarge filter coefficient α1 is decreased little by little, such that theflow rate value after stable flow rate calculation quickly becomesstable. Such processing is performed when 1>α1>α2>0.

[0247] When a stable flow rate which is subjected to filter processingwith a large filter coefficient is used, a response characteristic to aflow rate variation is decreased when a pulse causes a variation in theflow rate. However, by processing using two filters, even if the flowrate varies sharply when fluctuation occurs, such a variation can bequickly handled by using a flow rate calculated with a smaller flow ratecoefficient.

EMBODIMENT 25

[0248]FIG. 47 is a flowchart showing an operation of a flowmeteraccording to embodiment 25 of the present invention. Embodiment 25 isdifferent from embodiment 23 in that filter processing is performed onlywhen a flow rate value detected by the instantaneous flow rate detectionmeans is low.

[0249] As shown in FIG. 47, when an instantaneous flow rate measured bythe ultrasonic wave flow rate measurement means is smaller than apredetermined flow rate (e.g., 120 liter/hour), a stable flow rate canbe correctly measured by a filter process even when a pulse occurs.Furthermore, when the instantaneous flow rate measured by the ultrasonicwave flow rate measurement means is equal to or greater than thepredetermined flow rate, the ratio of a variation amplitude of flow ratemeasurement due to fluctuation is small. Thus, flow rate measurement canbe performed correctly without filter processing. Furthermore, since theflow rate is small, the filter processing is performed using a filtercoefficient a of a large value (e.g., α=0.999).

[0250] As described above, filter processing is performed only when theflow rate is low. Accordingly, a variation of flow rate can be quicklyhandled when the flow rate is high, and an influence of fluctuationwhich may be caused when the flow rate is low can be significantlysuppressed.

EMBODIMENT 26

[0251]FIG. 48 is a flowchart showing an operation of a flowmeteraccording to embodiment 26 of the present invention. Embodiment 26 isdifferent from embodiment 23 in that the filter processing meansmodifies a filter characteristic according to the flow rate value.

[0252] As shown in FIG. 48, filter coefficient α1 (e.g., (α1=0.9) isselected when an instantaneous flow rate measured by the ultrasonic waveflow rate measurement means is equal to or greater than a predeterminedvalue (e.g., 120 liter/hour), and filter coefficient α2 (e.g., α2=0.999)is selected when the instantaneous flow rate is smaller than thepredetermined value. When the flow rate is low, filter coefficient α2 isincreased, such that a stable flow rate is mainly measured. For example,when the flowmeter is used in a gas meter, leakage detection, equipmentdetermination, and pilot-burner registration are correctly performed. Onthe other hand, when the flow rate is high, filter coefficient al isdecreased, such that the measurement can be quickly modified accordingto a flow rate variation, whereby a response characteristic of anintegrated flow rate is improved.

[0253] As described above, the filter characteristic is modifiedaccording to the flow rate value. Filter processing is performed whenthe flow rate is low, and when the flow rate is high, a flow ratevariation can be quickly handled. Besides, when the flow rate is low, aninfluence of fluctuation can be considerably suppressed. As a result,when the flow rate is high, a response characteristic is increased. andwhen the flow rate is low, fluctuation can be suppressed.

EMBODIMENT 27

[0254]FIG. 49 is a flowchart showing an operation of a flowmeteraccording to embodiment 27 of the present invention. Embodiment 27 isdifferent from embodiment 23 in that the filter processing meansmodifies a filter characteristic at an interval of a flow ratemeasurement time of the ultrasonic wave flow rate measurement means.

[0255] As shown in FIG. 49, when the time period for which the flow rateis measured by the ultrasonic wave flow rate measurement means is long(e.g., 12 seconds), a small value is used as filter coefficient α1(e.g., α1=0.9) for filter processing. When the time period for which theflow rate is measured by the ultrasonic wave flow rate measurement meansis short, a large value is used as filter coefficient α2 (e.g.,α2=0.999) for filter processing.

[0256] The filter characteristic is modified according to the length ofthe time period for flow rate detection. When the measurement period isshort, a relaxed filter characteristic is used, and when the measurementperiod is long, a sharp filter characteristic is used, whereby avariation in the filter characteristic can be suppressed.

EMBODIMENT 28

[0257]FIG. 50 is a flowchart showing an operation of a flowmeteraccording to embodiment 28 of the present invention. Embodiment 28 isdifferent from embodiment 23 in that the filter characteristic ismodified such that a variation amplitude of a flow rate value calculatedby the stable flow rate calculation means is within a predeterminedrange.

[0258] As shown in FIG. 50, when a variation value of the flow ratewhich is obtained by stable flow rate calculation processing after thefilter processing is equal to or greater than a predetermined value(e.g., 1 liter/hour), the filter coefficient a is increased so as tocontrol the measurement such that the flow rate variation is suppressed.When the variation value of the flow rate is smaller than thepredetermined value, the filter coefficient a is decreased, and thefilter processing is performed under a state where a flow rate variationcan be dealt with.

[0259] The filter characteristic is appropriately modified such that avariation value obtained after the stable flow rate calculation means iswithin a predetermined range, whereby the flow rate variation can alwaysbe suppressed to be equal to or smaller than a predetermined value.

[0260] The increased amount of the filter coefficient is changedaccording to the variation value of the flow rate. When the variationamplitude is large, the increased amount of the filter coefficient isincreased. When the variation amplitude is small, the increased amountof the filter coefficient is decreased. With such an arrangement, avariation in the flow rate can be smoothly suppressed.

EMBODIMENT 29

[0261]FIG. 51 is a block diagram showing a flowmeter according toembodiment 29 of the present invention. Embodiment 29 is different fromembodiment 23 in that, in embodiment 29, heat-based flow rate detectionmeans 419 is used in place of the instantaneous flow rate detectionmeans.

[0262] As shown in FIG. 51, even when the heat-based flow rate detectionmeans 419 is used, a measured flow rate varies due to a pressurevariation if it is present. However, the same effects can be obtained byusing the methods described in embodiments 23-28, and the flow rate canbe measured with a high accuracy in a reliable manner.

EMBODIMENT 30

[0263]FIG. 52 is a block diagram showing a flowmeter according toembodiment 30 of the present invention.

[0264] The flowmeter of embodiment 30 includes: a flow rate measurementsection 500 through which a fluid to be measured flows; a pair ofultrasonic wave transducers 501 and 502 which are provided in the flowrate measurement section 500 and which transmit/receive an ultrasonicwave; a driver circuit 503 for driving the ultrasonic wave transducer502; a reception detecting circuit 504 which is connected to theultrasonic wave transducer 501 and which detects an ultrasonic wavesignal; a timer 505 for measuring a propagation time of an ultrasonicwave signal; a control section 507 for controlling the driver circuit503; a calculation section 506 for calculating the flow rate from anoutput of the timer; and periodicity change means 508 for sequentiallychanging a driving method of the driver circuit 503. Embodiment 30 isdifferent from the conventional examples in that the flowmeter ofembodiment 30 includes the periodicity change means 508. The details ofthe periodicity change means 508 are shown in FIG. 53. Reference numeral510 denotes a first oscillator, which herein generates an oscillationsignal of 500 kHz. Reference numeral 511 denotes a second oscillatorwhich generates an oscillation signal of 520 kHz. Reference numeral 512denotes a switching device which selects either an output of the firstoscillator 510 or an output of the second oscillator 511 based on anoutput of the control section 507 so as to output the selected output tothe driver circuit 503.

[0265] First, the control section 507 outputs a switching signal to theswitching device 512 to select the first oscillator 510. Then, the timer505 starts time measurement, and at the same time, the control section507 outputs a transmission start signal to the driver circuit 503.Receiving the transmission start signal, the driver circuit 503 drivesthe ultrasonic wave transducer 502 with the oscillation signal of 500kHz which is an input from the switching device 512. The operationsperformed thereafter are the same as those of the conventional examples.Next, the control section 507 outputs a switching signal to theswitching device 512 to select the second oscillator 511. Then,similarly to the previous flow rate measurement, time measurement of thetimer 505 is started, and at the same time, the control section 507outputs a transmission start signal to the driver circuit 503. Receivingthe transmission start signal, the driver circuit 503 drives theultrasonic wave transducer 501 with the oscillation signal of 520 kHzwhich is an input from the switching device 512.

[0266] Thereafter, the above operations are alternately continued so asto measure the flow rate. A reception detecting timing in suchmeasurement is shown in FIG. 54. As shown in this drawing, times whenthe 500 kHz signal and the 520 kHz signal are received are temporallyshifted. Reception detecting timings for the signals temporally shift asshown in curves (A) and (B) of FIG. 54. Thus, in this embodiment, thecontrol section controls the periodicity change means such that themeasurement frequency in the flow rate measurement is successivelychanged so as not to be kept constant. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed when theultrasonic wave is received. Therefore, a measurement error can bedecreased.

[0267] The periodicity change means is structured so as to switchinglyoutput a plurality of output signals having different frequencies, andthe control section operates such that the setting of frequency in theperiodicity change means is changed for each measurement, and thedriving frequency of the driver circuit is changed. Therefore, bychanging the driving frequency, the reception detecting timing can bechanged by a time corresponding to a periodic variation of a drivingsignal. Thus, noise which is in synchronization with a measurementfrequency or a transmission frequency of an ultrasonic wave is never inthe same phase but dispersed when the ultrasonic wave is received.Therefore, a measurement error can be decreased.

[0268] In embodiment 30, the driving frequency is changed by switchingtwo oscillators. However, the same effects can be obtained so long as anultrasonic wave transducer is driven while changing the drivingfrequency. The present invention can be achieved regardless of thenumber of oscillators, the driving frequency, and the structure of theswitching device.

EMBODIMENT 31

[0269]FIG. 55 is a block diagram showing a flowmeter according toembodiment 31 of the present invention.

[0270] The flowmeter of embodiment 30 includes: a flow rate measurementsection 500 through which a fluid to be measured flows; a pair ofultrasonic wave transducers 501 and 502 which are provided in the flowrate measurement section 500 and which transmit/receive an ultrasonicwave; a driver circuit 503 for driving one of the ultrasonic wavetransducers; a reception detecting circuit 504 which is connected to theother ultrasonic wave transducer and which detects an ultrasonic wave; acontrol section 507 for controlling the driver circuit 503 for apredetermined number of times such that the driver circuit 503 againdrives the ultrasonic wave transducers in response to an output of thereception detecting circuit 504; a timer 505 for measuring an elapsedtime for a predetermined number of times; a calculation section 506 forcalculating the flow rate from an output of the timer 505; andperiodicity change means 508 for sequentially changing a driving methodof the driver circuit 503.

[0271]FIG. 56 is a block diagram showing the details of the periodicitychange means.

[0272] Reference numeral 513 denotes a first delay, which generates anoutput signal 150 ps after receiving an input signal from the controlsection 507. Reference numeral 514 denotes a second delay, whichgenerates an output signal 150.5 μs after receiving an input signal fromthe control section 507. Reference numeral 515 denotes a third delay,which generates an output signal 151 us after receiving an input signalfrom the control section 507. Reference numeral 516 denotes a fourthdelay, which generates an output signal 151.5 μs after receiving aninput signal from the control section 507. Reference numeral 517 denotesa switching device which selects one of first to fourth delay outputsaccording to an output of the control section 507 and outputs theselected output to the driver circuit 503.

[0273] Embodiment 31 is different from embodiment 1 in that the controlsection 507 receives an output of the reception detecting circuit 504and drives the ultrasonic wave transducers again, and that thisoperation is repeated for a number of times which is a multiple of 4 (4is the delay set number), and during the repetition, the delay times ofthe periodicity change means 508 are sequentially switched every time anultrasonic wave is received.

[0274] In this structure, the control section 507 changes the setting ofthe delay every time reception of an ultrasonic wave is detected. Thus,in one measurement operation, reverberation of an ultrasonic wavetransmitted in an immediately-previous measurement and an influence oftailing of the ultrasonic wave transducers can be dispersed/averaged,whereby a measurement error can be decreased.

[0275] The cycle width which is changed by the periodicity change meanshas a value which is an equational division of the ultrasonic transducer(500 kHz). Thus, in an averaged value of the sum of values for all thesettings, an error which may be caused due to reverberation of anultrasonic wave and tailing of an ultrasonic wave sensor (i.e., noisehaving a cycle of 2 μs) can be minimized.

[0276] Furthermore, the number of times that measurement is repeated isa multiple of 4 (4 is a change number of the periodicity change means).Thus, within a single flow rate measurement cycle, measurement with eachof the predetermined values of the periodicity change means is performedthe same number of times. As a result, a variation of the measurementresult is suppressed, and accordingly, a reliable measurement result canbe obtained.

[0277] Furthermore, the order of patterns for changing the periodicityis the same for both measurement with an ultrasonic wave transmittedtoward the upstream side and measurement with an ultrasonic wavetransmitted toward the downstream side. Specifically, in the measurementwith an ultrasonic wave transmitted from upstream to downstream, thefirst delay, second delay, third delay, and fourth delay are selected inthis order, and then, the first delay is selected again; this cycle isrepeated. The measurement with an ultrasonic wave transmitted fromdownstream to upstream is performed such that the delays are necessarilyselected in the same order. With such an arrangement, the flow ratemeasurement with an ultrasonic wave transmitted toward the upstream sideand the flow rate measurement with an ultrasonic wave transmitted towardthe downstream side are always performed under the same conditions.Especially, even when there is a variation in the flow rate, a reliablemeasurement result can be obtained.

[0278] In embodiment 31, the delay time is changed by switching the fourdelays. The same effects can also be obtained so long as the ultrasonicwave transducers can be driven by changing the driving timing. Thepresent invention can be achieved regardless of the delay time, thenumber of delays, and the structure of the switching device.

[0279] In the above example, the delay times are inserted between thecontrol section 507 and the driver circuit 503. However, the sameeffects can also be obtained when the delay times are inserted betweenthe reception detecting circuit 504 and the control section 507.

[0280] In the above example, the width by which the delay is changed is2 μs the set number to be changed is 4, and the difference between theadjacent settings is 0.5 μs, which is a quarter of 2 μs. The presentinvention is not limited to these values. Each of these values may be avalue obtained by uniformly dividing a multiple of one cycle.

EMBODIMENT 32

[0281]FIG. 57A is a block diagram showing the periodicity change meansof the flowmeter according to embodiment 32 of the present invention.

[0282] Reference numeral 518 denotes an oscillator, and 519 denotes aphase converter. The oscillator outputs a signal at a frequency of 500kHz. The phase converter hastens or delays the phase of a signal of theoscillator according to a phase conversion signal from the controlsection 507, and outputs the signal with hastened or delayed phase. Forexample, when a phase control signal is Hi (high), the phase converteroutputs an output of the oscillator 518 as it is. When a phase controlsignal is Lo (low), the phase converter hastens the output signal of theoscillator 518 by 180° and outputs the hastened signal. The receptionsignals and reception detecting timings in these operations are shown inFIG. 57B.

[0283] As shown in this drawing, reception points are shifted by a ½cycle. That is, the shift time is 1 μs.

[0284] In this way, the reception detecting timing can be changed by atime period which is obtained by converting a phase variation of adriving signal into time by driving phase conversion. Thus, noise whichis in synchronization with a measurement frequency or a transmissionfrequency of an ultrasonic wave is never in the same phase but dispersedwhen the ultrasonic wave is received. Therefore, a measurement error canbe decreased.

[0285] In embodiment 32, the phase of a driving signal is changed byswitching between two phases. However, the same effects can be obtainedso long as the ultrasonic wave transducers can be driven by changing thedriving phase. The present invention can be achieved regardless of thephase to be changed and the structure of the switching device.

EMBODIMENT 33

[0286]FIG. 58 is a block diagram showing the periodicity change means ofthe flowmeter according to embodiment 33.

[0287] Reference numeral 520 denotes a first oscillator which outputs anoscillation signal of 500 kHz, which is a resonance frequency of anultrasonic wave transducer. Reference numeral 521 denotes a secondoscillator which outputs an oscillation signal of 200 kHz. Referencenumeral 522 denotes an ON/OFF circuit which determines whether or not anoutput of the second oscillator is output to a waveform adding section523 according to an ON/OFF switching signal from the control section507. The waveform adding section 523 synthesizes input waveforms tooutput the synthesized waveform to the driver circuit 503.

[0288] When the ultrasonic wave transducer is driven at a frequency ofabout 500 kHz, an ultrasonic wave signal having a large amplitude can bereceived. When the ultrasonic wave transducer is driven with only asignal component of 200 kHz, an ultrasonic wave signal can rarely bereceived. However, an oscillation signal of about 200 kHz is sometimesadded or sometimes not added to an oscillation frequency of about 500kHz. Such an irregular operation can cause a slight change in thefrequency of an ultrasonic wave signal to be received. As a result, thereception detecting timing can be changed. Thus, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed when theultrasonic wave is received. Therefore, a measurement error can bedecreased.

EMBODIMENT 34

[0289]FIG. 59 is a block diagram showing the periodicity change means ofthe flowmeter according to embodiment 34.

[0290] Reference numeral 520 denotes a first oscillator which outputs anoscillation signal of 500 kHz, which is a resonance frequency of anultrasonic wave transducer. Reference numeral 521 denotes a secondoscillator which outputs an oscillation signal of 200 kHz. Referencenumeral 524 denotes a phase conversion section which converts the phaseof an output signal of the second oscillator 521 by 180° according to anoutput of the control section 507, and outputs the signal with theconverted phase. Reference numeral 523 denotes a waveform adding sectionfor synthesizing input waveforms and outputting the synthesized waveformto the driver circuit 503.

[0291] When the ultrasonic wave transducer is driven at a frequency ofabout 500 kHz, an ultrasonic wave signal having a large amplitude can bereceived. When the ultrasonic wave transducer is driven with only asignal component of 200 kHz, an ultrasonic wave signal can rarely bereceived. However, the frequency of an ultrasonic wave signal, which isreceived by the ultrasonic wave transducer driven based on an additionsignal that is obtained by adding the phase of an oscillation signal ofabout 200 kHz which is changed by 180° in each measurement to anoscillation frequency of about 500 kHz, slightly changes. As a result,the reception detecting timing can be changed. Thus, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed when theultrasonic wave is received. Therefore, a measurement error can bedecreased.

EMBODIMENT 35

[0292]FIG. 60 is a block diagram showing the periodicity change means ofthe flowmeter according to embodiment 35.

[0293] Reference numeral 525 denotes a first oscillator which outputs anoscillation signal of 500 kHz, which is a resonance frequency of anultrasonic wave transducer. Reference numeral 526 denotes a secondoscillator which outputs an oscillation signal of 200 kHz. Referencenumeral 527 denotes a frequency conversion section which converts thefrequency of a signal input into the frequency converter, and outputsthe signal with the converted frequency. Herein, the frequencyconversion section 527 converts the frequency of the input signal to a½, i.e., 100 kHz. Reference numeral 523 denotes a waveform addingsection for synthesizing input waveforms and outputting the synthesizedwaveform to the driver circuit 503.

[0294] When the ultrasonic wave transducer is driven at a frequency ofabout 500 kHz, an ultrasonic wave signal having a large amplitude can bereceived. When the ultrasonic wave transducer is driven with only asignal component of 200 kHz or 100 kHz, an ultrasonic wave signal canrarely be received. However, the frequency of a received ultrasonic wavesignal, which is received by the ultrasonic wave transducer driven basedon an addition signal that is obtained by adding about 200 kHz to anoscillation frequency of about 500 kHz and an addition signal that isobtained by adding 100 kHz to an oscillation frequency of 500 kHz,slightly changes. As a result, the reception detecting timing can bechanged. Thus, noise which is in synchronization with a measurementfrequency or a transmission frequency of an ultrasonic wave is never inthe same phase but dispersed when the ultrasonic wave is received.Therefore, a measurement error can be decreased.

EMBODIMENT 36

[0295]FIG. 61 is a block diagram showing a flowmeter according toembodiment 36 of the present invention.

[0296] The flowmeter of embodiment 36 includes: a flow rate measurementsection 500 through which a fluid to be measured flows; a pair ofultrasonic wave transducers 501 and 502 which are provided in the flowrate measurement section 500 and which transmit/receive an ultrasonicwave; a driver circuit 503 for driving the ultrasonic wave transducer502; a reception detecting circuit 504 which is connected to theultrasonic wave transducer 501 and which detects an ultrasonic wavesignal; a first timer 527 for measuring a propagation time of anultrasonic wave signal; a second timer 528 for measuring a time periodfrom when the reception detecting circuit 504 receives a signal to whena value of the first timer 527 is changed; a control section 530 forcontrolling the driver circuit 503; a calculation section 506 forcalculating the flow rate from outputs of the first timer 527 and thesecond timer 528; a switching circuit 509 for switching connectionsbetween the ultrasonic wave transducers 501 and 502 and the drivercircuit 503 and the reception detecting circuit 504; a temperaturesensor 531 for measuring the temperature of the flowmeter and outputtingthe measured temperature to the control section 530; and a voltagesensor 532 for measuring the voltage of a power supply which powers theflowmeter.

[0297] The control section 530 outputs a measurement start signal to thedriving circuit 503 and, simultaneously, starts the time measurement ofthe first timer 527. The driving circuit 503 drives the ultrasonic wavetransducer 502 in response to a signal input so as to emit an ultrasonicwave. The emitted ultrasonic wave propagates in fluid and is received bythe ultrasonic wave transducer 501. The reception detecting circuit 504outputs the received ultrasonic wave signal to the first timer 527 andthe second timer 528. The first timer 527 receives an input signal fromthe reception detecting circuit 504 to stop the time measurement. Thesecond timer 528 receives an output of the reception detecting circuit504 to start time measurement, and then stops the time measurement insynchronization with a count-up timing output from the first timer 527.The calculation section 506 receives time measurement results of thefirst timer 527 and the second timer 528 and calculates the flow rate.

[0298]FIG. 62 shows operation timings of the first timer 527 and thesecond timer 528. As shown in FIG. 62, since the first timer 527 changesits state at a rising edge of a clock, an extra measurementcorresponding to portion A is performed. Since the measurementresolution of the first timer 527 is an interval B in FIG. 62, portion Awhich is counted as a measurement error is generated in eachmeasurement. The extra portion A is measured by the second timer 528 andsubtracted in the calculation section 506, whereby a propagation time ofan ultrasonic wave with high resolution is obtained, and a correct flowrate value is obtained.

[0299] Furthermore, the control section 530 starts the first timer 527and, simultaneously, outputs a start signal to the second timer 528 soas to start the second timer 528. At a time when the first timer 527counts up, an output signal, which is in synchronization with thecount-up timing, is output from the first timer 527 to the second timer528 so as to stop the second timer 528. At this time, the value of thesecond timer 528 is equal to a time measured within one clock time ofthe first timer 527. This time is processed in the calculation section506, a time corresponding to one clock of the second timer 528 isobtained, and the time corresponding to the one clock of the secondtimer 528, which is used in calculation, is corrected.

[0300] This operation is performed when an output of the temperaturesensor 531 or the power supply voltage sensor 532 varies so as to reachor exceed a set value. With such an arrangement, the second timer 528does not need to possess stability to the temperature and power supplyvoltage. As a result, inexpensive parts can be used. Furthermore, it isnot necessary to busily make corrections, and the amount of consumedpower can be suppressed to a low level.

[0301] Since the flow rate calculation is performed using a valueobtained by subtracting a value of the second timer 528 from a value ofthe first timer 527, the time measurement resolution is equal to that ofthe second timer 528. Further, since the operation time of the secondtimer 528 is very short, the amount of consumed power can be decreased.Thus, a flowmeter with high resolution which consumes a small amount ofpower can be realized. Furthermore, a correct flow rate measurement canbe achieved so long as the second timer 528 operates in a stable mannerafter the correction is made until flow rate measurement is performed.Therefore, a correct measurement can be performed even when the secondtimer 528 lacks long-term stability. Thus, a flowmeter with a highaccuracy can be realized with ordinarily-employed parts.

[0302] Furthermore, the temperature sensor 531 is provided. When anoutput of the temperature sensor 531 varies so as to reach or exceed aset value, the second timer 528 is corrected by the first timer 527.Thus, even when the second timer 528 has a characteristic which variesaccording to a variation in the temperature, the second timer 528 iscorrected every time a temperature variation occurs, whereby correctmeasurement can be performed. Furthermore, such a correction is madeonly when it is necessary, the amount of consumed power can bedecreased.

[0303] Furthermore, the voltage sensor 532 is provided. When an outputof the voltage sensor 532 varies so as to reach or exceed a set value,the second timer 528 is corrected by the first timer 527. Thus, evenwhen the second timer 528 has a characteristic which varies according toa variation in the power supply voltage, the second timer 528 iscorrected every time a variation occurs in power supply voltage, wherebycorrect measurement can be performed. Furthermore, such a correction ismade only when it is necessary, the amount of consumed power can bedecreased.

[0304] Furthermore, since such a correction is made, a crystaloscillator is used in a clock of the first timer 527, and a CRoscillation circuit is used in a clock of the second timer 528. A clockusing a crystal oscillator operates in a very stable manner. However, insuch a clock, a long time is consumed from when an operation is startedto when the operation becomes stable. Further, although a long-termstability cannot be secured with a CR oscillation circuit, a timer whoseoperation quickly becomes stable and which quickly operates in anon-synchronous mode can be readily realized with the CR oscillationcircuit. A crystal oscillator is used in a clock of the first timer 527,and a CR oscillation circuit is used in a clock of the second timer 528,whereby a stable timer with high resolution can be readily realized.

[0305] In FIG. 62 of embodiment 36, the second timer stops at a timewhen a clock of the first timer falls after the second timer starts tooperate. However, the present invention is not limited to this timingbecause a correct time can be obtained by a calculation to be performedlater so long as the timing is in synchronization with the first timer.

EMBODIMENT 37

[0306]FIG. 63 is a block diagram showing a flowmeter according toembodiment 37 of the present invention.

[0307] The flowmeter of embodiment 37 includes: a flow rate measurementsection 500; a pair of ultrasonic wave transducers 501 and 502 which areprovided in the flow rate measurement section 500 and whichtransmit/receive an ultrasonic wave; a driver circuit 503 for drivingthe ultrasonic wave transducer 502; a reception detecting circuit 504which is connected to the ultrasonic wave transducer 501 and whichdetects a received ultrasonic wave signal; a control section 507 forcontrolling the driver circuit 503 a predetermined number of times suchthat the driver circuit 503 again drives the ultrasonic wave transducer502 in response to an output of the reception detecting circuit 504; atimer 505 for measuring an elapsed time, a predetermined number oftimes; a calculation section 506 for calculating the flow rate from anoutput of the timer 505; and a delay section 533 which is frequencystabilizing means for sequentially changing a driving method of thedriver circuit 503.

[0308] The control section 507 outputs a measurement start signal to thedelay section 533 and, simultaneously, starts time measurement of thetimer 505. The delay section 533 outputs a signal to the driver circuit503 after a delay time which is set based on a setting signal from thecontrol section. In response to the signal input, the driver circuit 503drives the ultrasonic wave transducer 502 to emit an ultrasonic wave.The emitted ultrasonic wave propagates in fluid and is received by theultrasonic wave transducer 501. The reception detecting circuit 504outputs the received ultrasonic wave signal to the delay section 533,such that the driver circuit operates in a similar manner to that in aprevious cycle and transmit an ultrasonic wave signal again. The controlsection 507, which has received an output signal from the receptiondetecting circuit 504, counts such repetitious operation, and when thecount reaches a predetermined number of times, the control section 507stops the timer 505. The calculation section 506 receives a timemeasurement result of the timer 505 and calculates the flow rate.

[0309] The control section 507 receives a value of the timer 505 andsets the delay time of the delay section 533 so as to always beconstant. In this way, the control section 507 controls the measurementsuch that the measurement frequency is always constant. With such astructure, the measurement frequency is always constant even when avariation occurs in the propagation time. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is always in the same phase when the ultrasonicwave is received regardless of a variation in the propagation time.Therefore, a measurement error can be maintained as a constant value.Accordingly, the flow rate measurement can be stabilized even when thenoise has a very long periodic noise.

[0310] The control section 507 controls the delay section 533 so as tomaintain the measurement time to be constant. Therefore, the measurementfrequency can be maintained to be constant with a simple calculationwithout calculating a propagation time for each ultrasonic wavetransmission.

[0311] In embodiment 37, the measurement frequency is maintained to beconstant by changing the delay time. However, the same effects can beobtained so long as the measurement frequency is constant. Specifically,the same effects can be obtained by using a different method, e.g., bychanging the distance between the ultrasonic wave transducers.

[0312] Since a propagation time of an ultrasonic wave from upstream todownstream is different from a propagation time of an ultrasonic wavefrom downstream to upstream when there is a flow, a different delay canbe set for stabilizing the measurement frequency.

[0313] Furthermore, when a flow rate is large, and an error caused byperiodic noise is negligible, an operation of the periodicitystabilizing means is stopped, whereby the amount of consumed electricpower can be reduced.

[0314] Furthermore, at an initial stage of measurement, the flow rate ismeasured while changing the setting of the measurement frequencystabilizing means, whereby a measurement frequency with which a smallestvariation is caused in a measurement result by a measurement frequencyvariation is set as a target measurement frequency. With such anarrangement, a further stable measurement result can be obtained.

[0315] Industrial Applicability

[0316] As described above, according to a flowmeter of the presentinvention, the following effect can be obtained.

[0317] In order to solve the above problems, a flowmeter of the presentinvention includes: transmission/reception means provided in a flow pathfor performing transmission/reception using a state change of fluid;repetition means for repeating the transmission/reception; timemeasurement means for measuring a time or propagation repeated by therepetition means; flow rate detection means for detecting a flow ratebased on a value of the time measurement means; and number-of-timeschange means for changing to a predetermined number of repetition times.The number of repetition times is changed to an optimum number such thatan influence of a variation of a flow can be suppressed. As a result,reliable flow rate measurement with a high accuracy can be achieved.

[0318] The flowmeter includes a pair of transmission/reception meanswhich utilize propagation of an ultrasonic wave as the state change offluid. Thus, by using the sonic wave transmission/reception means,propagation of a sonic wave can be performed even when a state changeoccurs in the fluid. Moreover, by changing the number of repetitiontimes to an optimum number for the variation, reliable flow ratemeasurement with a high accuracy can be achieved.

[0319] The flowmeter includes transmission/reception means whichutilizes propagation of heat as the state change of fluid. Thus, byusing the heat transmission/reception means, propagation of heat can beperformed even when a state change occurs in the fluid. Moreover, bychanging the number of repetition times to an optimum number for thevariation, reliable flow rate measurement with a high accuracy can beachieved.

[0320] The flowmeter includes: elapsed time detection means fordetecting halfway information for a propagation time which is repeatedlymeasured by the repetition means; frequency detection means fordetecting a frequency of a flow rate variation from information of theelapsed time detection means; and number-of-times change means forsetting a measurement time so as to be substantially a multiple of thefrequency detected by the frequency detection means. Thus, it is notnecessary to provide specific detection means. Before flow ratedetection is performed, the frequency of a variation is detected frothhalfway information of the time measurement means, and the measurementtime can be set so as to be a multiple of a cycle of the frequency. As aresult, reliable flow rate measurement with a high accuracy can beachieved.

[0321] The flowmeter includes: data holding means for holding at leastone or more propagation time of repeatedly-performedtransmission/reception which is obtained by the elapsed time detectionmeans; and frequency detection means for detecting a frequency bycomparing the data held by the data holding means and measuredpropagation time data. Time measurement information at each moment isheld and compared by the data holding means, whereby the frequency canbe detected.

[0322] The number-of-times change means is operated in predeterminedprocessing. Since the number-of-times change means is operated only whenpredetermined processing is performed, the processing in thenumber-of-times change means can be limited to the required minimum.Thus, the amount of consumed power can be considerably reduced.

[0323] The number-of-times change means is operated at eachpredetermined flow rate measurement. Thus, the number of repetitiontimes is changed at every predetermined flow rate measurement, wherebythe flow rate can be measured with a high accuracy in a stable mannereven in a flow that varies greatly.

[0324] The number-of-times change means is performed before flow ratemeasurement processing. Since the number of repetition times is set to apredetermined number of times before flow rate measurement is performed,the flow rate measurement can be performed with a high accuracy in areliable manner.

[0325] Predetermined processing includes operations of abnormalitydetermination means for determining abnormality in flow rate from themeasured flow rate; and flow rate management means for managing a usestate for a flow rate from a measured flow rate. Since the number ofrepetition times is changed only when the abnormality determinationprocessing and the flow rate management processing are performed, theprocessing of changing the number of repetition times is limited to therequired minimum. Thus, the amount of consumed power can be decreased.

[0326] The number of repetition times which is adjusted the frequencyobtained by the frequency detection means is used in next flow ratemeasurement. Since the number of repetition times is used in the nextmeasurement, it is not necessary to perform repetitious measurement forfrequency detection. Thus, the amount of consumed power can bedecreased.

[0327] The number-of-times change means is operated when the measuredflow rate is lower than a predetermined flow rate. Since the number ofrepetition times is changed only when the flow rate is equal to or lowerthan a predetermined flow rate, but this processing is not performedwhen the flow rate is high, the amount of consumed power can bedecreased.

[0328] A flowmeter of the present invention includes:transmission/reception means provided in a flow path for performingtransmission/reception using a state change of fluid; time measurementmeans for measuring a propagation time transmitted/received by thetransmission/reception means; flow rate detection means for detecting aflow rate based on a value of the time measurement means; variationdetection means for measuring a variation in the flow path by thetransmission/reception means; and measurement control means for startingmeasurement in synchronization with a timing of a variation of thevariation detection means. Since a variation in the flow path ismeasured by transmission/reception means, it is not necessary to provideanother sensor for detecting a variation. Thus, the size of theflowmeter can be decreased, and the structure of the flow path can besimplified. In addition, the flow rate can be measured with a highaccuracy in a reliable manner within a short space of time even when avariation occurs.

[0329] The flowmeter includes a pair of transmission/reception meanswhich utilize propagation of an ultrasonic wave as the state change offluid. Thus, a state change of fluid can be detected by the sonic wavetransmission/reception means. Accordingly, the measurement can bestarted in synchronization with a timing of variation. As a result, theflow rate can be measured with a high accuracy in a reliable manner.

[0330] The flowmeter includes transmission/reception means whichutilizes propagation of heat as the state change of fluid. Thus, a statechange of fluid can be detected by the heat transmission/receptionmeans. Accordingly, the measurement can be started in synchronizationwith a timing of variation. As a result, the flow rate can be measuredwith a high accuracy in a reliable manner.

[0331] The flowmeter includes: first vibration means and secondvibration means provided in a flow path for transmitting/receiving ansonic wave; switching means for switching an transmission/receptionoperation of the first vibration means and the second vibration means;variation detection means for detecting a pressure variation in a flowpath of at least one of the first vibration means and the secondvibration means; time measurement means for measuring a propagation timeof a sonic wave transmitted/received by the first vibration means andthe second vibration means; measurement control means for performingsynchronous control where, when an output of the variation detectionmeans shows a predetermined change, the measurement means measures afirst measurement time T1 of propagation from the first vibration meansat an upstream side in the flow path to the second vibration means at adownstream side in the flow path, and when the output of the variationdetection means shows a change opposite to the predetermined change, themeasurement means measures a second measurement time T2 of propagationfrom the second vibration means at a downstream side in the flow path tothe first vibration means at an upstream side in the flow path; flowrate detection means for calculating a flow rate using the firstmeasurement time T1 and the second measurement time T2. Since themeasurement is performed at a time when a change in a pressure variationis inverted, the phases of the pressure variation and the timing of themeasurement can be shifted. As a result, a measurement error caused by apressure variation can be offset.

[0332] The flowmeter includes: measurement control means for performingmeasurement control where measurement of the first measurement time T1is started when an output of the variation detection means shows apredetermined change and measurement of the second measurement time T2is started when the output of the variation detection means shows achange opposite to the predetermined change, and measurement controlwhere, in a next measurement, measurement of the first measurement timeT1 is started when the output of the variation detection means shows achange opposite to the predetermined change and measurement of thesecond measurement time T2 is started when the output of the variationdetection means shows the predetermined change; and flow ratecalculation means for calculating the flow rate by successivelyaveraging a first flow rate obtained by using the previous firstmeasurement time T1 and previous second measurement time T2 whilealternately changing start of measurement and a second flow rateobtained by using next first measurement time T1 and next secondmeasurement time T2. Thus, the timing for measurement is changed asdescribed above in order to perform measurement for the firstmeasurement time T1 and the second measurement time T2. As a result,even when a pressure variation is asymmetrical between a high pressureside and a low pressure side, an influence of such a pressure variationcan be offset.

[0333] The flowmeter includes repetition means for performingtransmission/reception a plurality of times. Thus, averaging can beperformed by increasing the number of times of measurement, and as aresult, reliable flow rate measurement can be performed.

[0334] The flowmeter includes repetition means for performingtransmission/reception a plurality of times over a time period which isa multiple of a variation cycle. Thus, a pressure variation can beaveraged by measuring according to the variation frequency. As a result,a stable flow rate can be measured.

[0335] The flowmeter includes repetition means for startingtransmission/reception measurement when an output of the variationdetection means shows a predetermined change and repeating thetransmission/reception measurement with a sonic wave until the output ofthe variation detection means shows the same change as the predeterminedchange. Thus, the start and stop of the measurement can be madeconformable to the frequency of a pressure variation. Therefore, avariation frequency can be measured, and a pressure variation isaveraged. As a result, a stable flow rate can be measured.

[0336] The flowmeter includes selection means for switching a case wherethe first vibration means and second vibration means are used fortransmission/reception of a sonic wave and a case where the firstvibration means and second vibration means are used for detection of apressure variation. Thus, at least one of the first vibration means andthe second vibration means is used for pressure detection. As a result,both the flow rate measurement and the pressure measurement can besimultaneously achieved.

[0337] The flowmeter includes variation detection means for detecting acomponent of an alternating component of a variation waveform which isin the vicinity of zero. Thus, a variation is detected in the vicinityof a zero component of the variation, and hence the measurement can bestarted in the vicinity of zero variation within a time to perform flowrate measurement. Therefore, by performing the flow rate measurementwithin a time when a variation is small, the measurement can bestabilized even when a variation occurs in a fluid.

[0338] The flowmeter includes: frequency detection means for detectingthe frequency of a signal of the variation detection means; andmeasurement control means for starting measurement only when thefrequency detected by the frequency detection means is a predeterminedfrequency. Thus, by starting the measurement only when the frequency isa predetermined frequency, measurement can be performed when apredetermined variation occurs. As a result, a stable flow rate can bemeasured.

[0339] The flowmeter includes detection cancellation means forautomatically starting measurement after a predetermined time periodwhen a signal of the variation detection means is not detected. Thus,even after a variation disappears, the flow rate can be automaticallymeasured when a predetermined time arrives.

[0340] The transmission/reception means and the first and secondvibration means include piezoelectric transducers. Thus, when thepiezoelectric transducer is used, an ultrasonic wave is used fortransmission/reception while a pressure variation can be detected.

[0341] A flowmeter of the present invention includes:transmission/reception means provided in a flow path for performingtransmission/reception using a state change of fluid; repetition meansfor repeating signal propagation by the transmission/reception means;time measurement means for measuring a propagation time duringrepetition by the repetition means; flow rate detection means fordetecting a flow rate based on a value of the time measurement means;variation detection means for detecting a fluid variation in a flowpath; measurement control means for controlling each of the above means;and measurement monitoring means for monitoring abnormality in each ofthe above means. Thus, when there is a variation in a flow in the flowpath, the flow rate is measured according to the variation, whileabnormality can be quickly detected by the measurement monitoring means.Accordingly, handling of abnormality can be correctly performed, and ameasured value becomes stable. As a result, the flow rate can bemeasured with a high accuracy, and the reliability of the measurementcan be improved.

[0342] The flowmeter includes a pair of transmission/reception meanswhich utilize propagation of an ultrasonic wave as the state change offluid. Since a sonic wave is used, the flow rate measurement can beperformed even when there is a variation in fluid. Further, handling ofabnormality can be correctly performed by the measurement monitoringmeans. As a result, the reliability of the measurement can be improved.

[0343] The flowmeter includes transmission/reception means whichutilizes propagation of heat as the state change of fluid. Since heatpropagation is used, the flow rate measurement can be performed evenwhen there is a variation in fluid. Further, handling of abnormality canbe correctly performed by the measurement monitoring means. As a result,the reliability of the measurement can be improved.

[0344] The flowmeter includes: a pair of transmission/reception meansprovided in a flow path for transmitting/receiving a sonic wave;repetition means for repeating signal propagation of thetransmission/reception means; time measurement means for measuring apropagation time of a sonic wave during the repetition by the repetitionmeans; flow rate detection means for detecting the flow rate based on avalue of the time measurement means; variation detection means fordetecting a fluid variation in a flow path; measurement control meansfor controlling each of the above means; and measurement monitoringmeans for monitoring abnormality in a start signal which directs startof transmission of a sonic wave at a first output signal of thevariation detection means after a measurement direction signal of themeasurement control means, and abnormality in an end signal whichdirects end of repetition of the transmission/reception of the sonicwave at second output signal of the variation detection means. Thus,when there is a variation in fluid in the flow path, the measurement canbe performed in synchronization with the frequency of the variation, andabnormality can be detected by the measurement monitoring means.Therefore, a flow rate can be measured with a high accuracy, and areliable measured value can be obtained. In addition, handling ofabnormality can be correctly performed, and the reliability of themeasured flow rate value can be improved.

[0345] The flowmeter includes measurement monitoring means for directinga start of transmission of a sonic wave after a predetermined time whena start signal is not generated within a predetermined time period aftera direction of the measurement control means. Thus, even when there isno variation, and there is no start signal within a predetermined timeperiod, the flow rate can be measured at every predetermined time, andloss of data can be prevented.

[0346] The flowmeter includes measurement monitoring means for directingstart of transmission of a sonic wave after a predetermined time when astart signal is not generated within a predetermined time period after adirection of the measurement control means, and for performingmeasurement a predetermined number of repetition times. Thus, even whenthere is no variation, and there is no start signal within apredetermined time period, the flow rate can be measured for apredetermined number of repetition times at every predetermined time,and loss of data can be prevented.

[0347] The flowmeter includes measurement monitoring means which doesnot perform measurement until a next direction of the measurementcontrol means when a start signal is not generated within apredetermined time period after a direction of the measurement controlmeans. By suspending the operation until a next measurement direction,unnecessary measurement is not performed, whereby the amount of consumedpower can be decreased.

[0348] The flowmeter includes measurement monitoring means whichterminates reception of a sonic wave when an end signal is not generatedwithin a predetermined time after a start signal. Since the reception ofthe sonic wave is forcibly terminated, the measurement is not suspendedwhile waiting for the end signal. Thus, the measurement can proceed to anext process, and a stable measurement operation can be performed.

[0349] The flowmeter includes measurement monitoring means whichterminates reception of a sonic wave and outputs a start signal again,when an end signal is not generated within a predetermined time after astart signal. Since the reception of the sonic wave is forciblyterminated, the measurement is not suspended while waiting for the endsignal. Further, a start signal is output again so as to performre-measurement. Thus, a stable measurement operation can be performed.

[0350] The flowmeter includes measurement monitoring means for stoppingtransmission/reception processing when abnormality occurs in the numberof repetition times. Since the measurement is stopped when the number ofrepetition times is abnormal, only data with a high accuracy can be usedto perform flow rate measurement.

[0351] The flowmeter includes measurement monitoring means whichcompares a first number of repetition times for measurement where asonic wave is transmitted from a first one of the pair oftransmission/reception means and received by the secondtransmission/reception means and a second number of repetition times formeasurement where a sonic wave is transmitted from the secondtransmission/reception means and received by the firsttransmission/reception means, and again outputs a start signal when thedifference between the first and second numbers of repetition times isequal to or greater than a predetermined number of times. Thus,re-measurement is performed when the number of repetition times isgreatly different, whereby measurement with a high accuracy can beperformed with a stable variation frequency.

[0352] The flowmeter includes repetition means for setting the number ofrepetition times such that a first number of repetition times formeasurement where a sonic wave is transmitted from first one of the pairof transmission/reception means and received by the secondtransmission/reception means is equal to a second number of repetitiontimes for measurement where a sonic wave is transmitted from the secondtransmission/reception means and received by the firsttransmission/reception means. Thus, by employing the same number ofrepetition times, a predetermined flow rate measurement can be performedeven when a variation frequency is unstable.

[0353] The flowmeter includes measurement monitoring means formonitoring the number of times that a start signal is output again so asto be limited to a predetermined number of times or less, such that theoutputting of the start signal is not permanently repeated. Thus, bylimiting the number of times of re-measurement, the processing isprevented from continuing permanently. As a result, stable flow ratemeasurement can be performed.

[0354] The flowmeter measures a flow rate from a difference betweeninverse numbers of propagation times measured while repeatingtransmission/reception of an ultrasonic wave a plurality of number oftimes. Thus, when an ultrasonic wave is used, transmission/reception canbe performed without being affected by a variation frequency in the flowpath. Further, the flow rate is measured from the difference of inversenumbers of propagation times which are measured while repeating thetransmission/reception, whereby even a variation of a long cycle can bemeasured by units of one cycle. In addition, the difference of thepropagation times which is caused by a variation can be offset by usingthe difference of inverse numbers.

[0355] A flowmeter of the present invention includes: instantaneous flowrate detection means for detecting an instantaneous flow rate;fluctuation determination means for determining whether or not there isa pulse in a flow rate value; and at least one or more stable flow ratecalculation means for calculating a flow rate value using differentmeans according to a determination result of the fluctuationdetermination means. Thus, by determining a variation in a measured flowrate and switching the flow rate calculation means, the flow rate can becalculated by one flow rate measurement means according to the amount ofthe variation in a reliable manner.

[0356] A flowmeter of the present invention includes: instantaneous flowrate detection means for detecting an instantaneous flow rate; filterprocessing means for performing digital-filter processing of a flow ratevalue; and stable flow rate calculation means for calculating a flowrate value using the filter processing means. Thus, when the digitalfilter processing is performed, a calculation equivalent to an averagingprocess can be performed without using a large number of memories forstoring data. Moreover, the filter characteristic can be modified bychanging one variable, i.e., a filter coefficient.

[0357] The flowmeter includes stable flow rate calculation means forcalculating a stable flow rate value using the digital filter processingmeans when the fluctuation determination means determines that there isa pulse. Thus, when a pulse occurs, a sharp filter characteristic isselected so as to render a large pulse stable, and the filter processingcan be performed only when a pulse occurs.

[0358] The fluctuation determination means determines whether or not avariation amplitude of a flow rate value is equal to or greater than apredetermined value. Thus, a pulse can be determined based on thevariation amplitude of the pulse, whereby the filter processing can bemodified according to the variation amplitude of the pulse.

[0359] The filter processing means modifies a filter characteristicaccording to a variation amplitude of a flow rate value. Since thefilter characteristic is changed according to the variation amplitude ofa flow rate value, the filter characteristic can be quickly modified soas to be a sufficiently relaxed filter characteristic that allows avariation according to a variation in a flow rate when the variation issmall, and when the variation is large, a sharp filter characteristic isselected such that a variation of the flow rate due to a pulse can besignificantly suppressed.

[0360] The filter processing is performed only when a flow rate valuedetected by the instantaneous flow rate detection means is low. Sincethe filter processing is performed only when the flow rate is low, avariation of the flow rate can be quickly handled when the flow rate ishigh, and an influence of fluctuation which is caused when the flow rateis low can be significantly suppressed.

[0361] Filter processing means modifies a filter characteristicaccording to a flow rate value. Since the filter characteristic ischanged according to the flow rate value, filter processing is performedonly when the flow rate is low, a variation of the flow rate can bequickly handled when the flow rate is high, and an influence offluctuation which is caused when the flow rate is low can besignificantly suppressed.

[0362] Filter processing means modifies a filter characteristicaccording to an interval of a measurement time of the instantaneous flowrate detection means. Thus, by changing the filter characteristicaccording to an interval of the flow rate detection time, the variationcan be suppressed with a relaxed filter characteristic when themeasurement interval is short or with a sharp filter characteristic whenthe measurement interval is long.

[0363] The flowmeter includes filter processing means which modifies afilter characteristic such that a cut-frequency of the filtercharacteristic becomes high when the flow rate is high, and whichmodifies a filter characteristic such that the filter characteristic hasa low cut-off frequency when the flow rate is low. Thus, the responsecharacteristic is increased when the flow rate is high, and thefluctuation is suppressed when the flow rate is low.

[0364] A filter characteristic is modified such that a variationamplitude of a flow rate value calculated by the stable flow ratecalculation means is within a predetermined value range. Since thefilter characteristic is modified such that the variation amplitude iswithin a predetermined value range, the flow rate variation can besuppressed so as to be always equal to or smaller than a predeterminedvalue.

[0365] An ultrasonic wave flowmeter which detects a flow rate by usingan ultrasonic wave is used as the instantaneous flow rate detectionmeans. Thus, by using an ultrasonic wave flowmeter, an instantaneousflow rate can be measured even when a large flow rate variation occurs.Thus, from the flow rate value, a stable flow rate can be calculated.

[0366] A heat-based flowmeter is used as the instantaneous flow ratedetection means. When the heat-based flowmeter is used, an instantaneousflow rate can be measured even when a large flow rate variation occurs.Thus, a stable flow rate can be calculated from the flow rate value.

[0367] Further, the control section controls the periodicity changemeans so as to sequentially change the frequency of the measurement inthe flow rate measurement such that the frequency of the measurement isnot kept constant. Thus, noise which is in synchronization with ameasurement frequency or a transmission frequency of an ultrasonic waveis never in the same phase but dispersed when the ultrasonic wave isreceived. Therefore, a measurement error can be decreased.

[0368] Furthermore, the flowmeter of the present invention includesperiodicity change means for sequentially changing the driving method ofthe driver circuit. In response to receipt of an output of the receptiondetecting circuit, the control section modifies the periodicity changemeans every time the reception detecting circuit detects a receipt of anultrasonic wave such that the frequency of the measurement is not keptconstant. Thus, the periodicity change means can be operated with aplurality of settings for measurement within one flow rate measurementcycle. As a result, noise is dispersively averaged in a measurementresult, and a reliable measurement result can be obtained.

[0369] The periodicity change means switchingly outputs a plurality ofoutput signals having different frequencies; and the control sectionchanges a frequency setting of the periodicity change means at everymeasurement so as to change a driving frequency of the driver circuit.Thus, by changing the driving frequency, the reception detecting timingcan be changed by a time corresponding to a frequency variation of adriving signal. Thus, noise which is in synchronization with ameasurement frequency or a transmission frequency of an ultrasonic waveis never in the same phase but dispersed when the ultrasonic wave isreceived. Therefore, a measurement error can be decreased.

[0370] The periodicity change means outputs output signals having thesame frequency and a plurality of different phases; and the controlsection operates such that a phase setting for the output signal of theperiodicity change means is changed at every measurement and a drivingphase of the driver circuit is changed. Thus, by changing the drivingphase, the reception detecting timing can be changed by a timecorresponding to a phase variation of a driving signal. Thus, noisewhich is in synchronization with a measurement frequency or atransmission frequency of an ultrasonic wave is never in the same phasebut dispersed when the ultrasonic wave is received. Therefore, ameasurement error can be decreased.

[0371] The periodicity change means outputs a synthesized signalobtained by superposing a signal of a first frequency which is anoperation frequency of the ultrasonic wave transducers and a signal of asecond frequency which is different from the first frequency; and thecontrol section outputs, through the driver circuit, at everymeasurement, an output signal where the second frequency of theperiodicity change means is changed. Thus, the periodicity of the flowrate measurement can be disturbed. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed when theultrasonic wave is received. Therefore, a measurement error can bedecreased.

[0372] The periodicity change means switches the setting between a casewhere there is a second frequency and a case where there is not a secondfrequency. Thus, since the reception detecting timing is changed bychanging the vibration of the ultrasonic wave transducer that transmitsan ultrasonic wave, the periodicity of the flow rate measurement can bedisturbed. As a result, noise which is in synchronization with ameasurement frequency or a transmission frequency of an ultrasonic waveis never in the same phase but dispersed when the ultrasonic wave isreceived. Therefore, a measurement error can be decreased.

[0373] The periodicity change means changes the phase setting of thesecond frequency. Thus, since the reception detecting timing is changedby changing the vibration of the ultrasonic wave transducer thattransmits an ultrasonic wave, the periodicity of the flow ratemeasurement can be disturbed. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed/averagedwhen the ultrasonic wave is received. Therefore, a measurement error canbe decreased.

[0374] The periodicity change means changes the frequency setting of thesecond frequency. Thus, since the reception detecting timing is changedby changing the vibration of the ultrasonic wave transducer thattransmits an ultrasonic wave, the periodicity of the flow ratemeasurement can be disturbed. As a result, noise which is insynchronization with a measurement frequency or a transmission frequencyof an ultrasonic wave is never in the same phase but dispersed when theultrasonic wave is received. Therefore, a measurement error can bedecreased.

[0375] The periodicity change means includes a delay section capable ofsetting different delay times; and the control section changes thesetting of the delay at each transmission of an ultrasonic wave or ateach receipt detection of an ultrasonic wave. Thus, in one measurementoperation, reverberation of an ultrasonic wave transmitted in animmediately-previous measurement and an influence of tailing of theultrasonic wave transducers can be dispersed, whereby a measurementerror can be decreased.

[0376] The cycle width changed by the periodicity change means is amultiple of a value corresponding to a variation of a propagation timewhich is caused by a measurement error. Thus, when the measured valuesfor all the settings are summed up and averaged, an error can besuppressed to a minimum.

[0377] The cycle width changed by the periodicity change means is equalto a cycle of a resonance frequency of the ultrasonic wave transducers.Thus, in a value obtained by summing up and averaging the measuredvalues for all the settings, a measurement error which may be caused byreverberation of an ultrasonic wave or tailing of the ultrasonic wavetransducers is minimum. Thus, the measurement error can be decreased.

[0378] The order of patterns for changing the periodicity is the samefor both measurement in a upstream direction and measurement in adownstream direction. Thus, the measurement with an ultrasonic wavetransmitted toward the upstream side and the measurement with anultrasonic wave transmitted toward the downstream side are alwaysperformed under the same conditions. Hence, even when there is avariation in the flow rate, a reliable measurement result can beobtained.

[0379] The predetermined number of times is a multiple of a changenumber of the periodicity change means. Thus, all the setting values ofthe periodicity change means are uniformly set within a single flow ratemeasurement operation. As a result, a reliable measurement result can beobtained.

[0380] Further, a time period from receipt detection to a next count-uptime is measured by a second timer, whereby measurement can be performedwith a resolution higher than that of a first timer. Furthermore, theamount of consumed power can be decreased in comparison to a flowmeterhaving the same resolution, because it is necessary to operate thesecond timer for only a short time period after the receipt detection.

[0381] Furthermore, since the second timer is corrected by the firsttimer, the second timer only needs to possess a short-term stability.Thus, it is not necessary to use a special part. Therefore, a flowmeterwith high resolution can be readily realized.

[0382] Furthermore, since the second timer is corrected by the firsttimer when an output of a temperature sensor varies so as to be equal toor greater than a set value, the flowmeter of the present invention canbe used even when the second timer has a characteristic which variesaccording to a variation of temperature.

[0383] Further still, since the second timer is corrected by the firsttimer when an output of a voltage sensor varies so as to be equal to orgreater than a set value, the flowmeter of the present invention can beused even when the second timer has a characteristic which variesaccording to a variation of voltage.

[0384] A flowmeter of the present invention includes: a flow ratemeasurement section through which fluid to be measured flows; a pair ofultrasonic wave transducers provided in the flow rate measurementsection for transmitting/receiving an ultrasonic wave; a driver circuitfor driving one of the ultrasonic wave transducers; a receptiondetecting circuit connected to the other ultrasonic wave transducer fordetecting an ultrasonic wave signal; a control section for controllingthe driver circuit for a predetermined number of times so as to drivethe ultrasonic wave transducers again in response to an output of thereception detecting circuit; a timer for measuring an elapsed time forthe predetermined number of times; a calculation section for calculatinga flow rate from an output of the timer; and periodicity stabilizingmeans for sequentially changing a driving method of the driver circuit,wherein the control section controls the periodicity stabilizing meanssuch that a measurement frequency is always maintained to be constant.With this structure, the measurement frequency is always constant evenwhen a propagation time varies. Thus, noise which is in synchronizationwith a measurement frequency or a transmission frequency of anultrasonic wave is always in the same phase when the ultrasonic wave isreceived regardless of a variation in the propagation time. Therefore, ameasurement error can be maintained as a constant value. Accordingly,the flow rate measurement can be stabilized even when the noise has avery long periodic noise.

[0385] The control section includes periodicity stabilizing means formedby a delay section capable of setting different delay times; and thecontrol section changes an output timing of the driver circuit byswitching the delay times. Since the measurement frequency is maintainedto be constant by changing the delay time, the measurement frequency canbe stabilized without giving an influence to driving of the ultrasonicwave transducers.

[0386] The control section controls the driver circuit such that ameasurement time is maintained to be constant. Thus, the measurementfrequency can be maintained to be constant with a simple calculationwithout calculating a propagation time for each ultrasonic wavetransmission.

1. a flowmeter comprising: instantaneous flow rate detection means fordetecting an instantaneous flow rate of fluid; filter processing meansfor removing a pulse flow rate component of the instantaneous flow rateof the fluid by digital filter-processing the instantaneous flow rate ofthe fluid which is detected by the instantaneous flow rate detectionmeans; and stable flow rate calculation means for calculating a stableflow rate of the fluid based on an output from the filter processingmeans.
 2. A flowmeter according to claim 1, further comprisingfluctuation determination means for determining whether theinstantaneous flow rate of the fluid pulses or not, wherein, when thefluctuation determination means determines that the instantaneous flowrate of the fluid pulses, the stable flow rate calculation meanscalculates a stable flow rate of the fluid based on an output from thefilter processing means.
 3. A flowmeter according to claim 2, whereinthe fluctuation determination means determines whether the instantaneousflow rate of the fluid pulses or not, by determining whether or not avariation amplitude of the instantaneous flow rate of the fluid is equalto or greater than a predetermined value.
 4. A flowmeter according toclaim 1, wherein the filter processing means modifies a filtercharacteristic according to a variation amplitude of the instantaneousflow rate of the fluid.
 5. A flowmeter according to claim 1, wherein,when the instantaneous flow rate of the fluid which is detected by theinstantaneous flow rate detection means is lower than a predeterminedflow rate, the filter processing means removes a pulse component of theinstantaneous flow rate of the fluid.
 6. A flowmeter according to claim1, wherein the filter processing means modifies a filter characteristicaccording to the instantaneous flow rate of the fluid.
 7. A flowmeteraccording to claim 1, wherein the filter processing means modifies afilter characteristic according to an interval of measurement times ofthe instantaneous flow rate detection means.
 8. A flowmeter according toclaim 7, wherein, when the flow rate is high, the filter processingmeans modifies a filter characteristic such that a cut-off frequency ofthe filter characteristic becomes high, and when the flow rate is low,the filter processing means modifies the filter characteristic such thatthe cut-off frequency of the filter characteristic becomes low.
 9. Aflowmeter according to claim 1, wherein the filter processing meansmodifies a filter characteristic such that a variation amplitude of thestable flow rate calculated by the stable flow rate calculation means iswithin a predetermined value range.
 10. A flowmeter according to claim1, wherein the instantaneous flow rate detection means detects theinstantaneous flow rate by using an ultrasonic wave.
 11. A flowmeteraccording to claim 1, wherein the instantaneous flow rate detectionmeans detects the instantaneous flow rate by using heat.